Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/27/19
Area Forecast Discussion
National Weather Service Honolulu HI
400 PM HST Thu Dec 26 2019
.SYNOPSIS...
A dissipating front will maintain wet conditions over portions of
the Big Island tonight. Northerly winds will build down the rest
of the island chain tonight with showers favoring north slopes of
Kauai and Oahu. Showers will favor windward slopes of all islands
as locally breezy trade winds develop statewide on Friday, then
shift out of the east during the weekend. Trade winds will
decrease on Wednesday.
&&
.DISCUSSION...
A stalled front is falling apart near the Big Island this
afternoon. Moisture along the front is being pushed by southerly
winds onto Kau and the south slopes of Puna, where widespread
shower activity has persisted through the day. The upper level
trough that was driving the front is moving off to the east,
though enough instability lingers to produce a few heavy showers
over South Point.
A post-frontal flow is slowly veering out of the southwest over
Maui and west-northwest near Kauai. The afternoon Lihue sounding
and recent aircraft data show an inversion continuing to build
between 5,000 and 6,500 ft, leading to rather stable and mainly
dry conditions. However, though there are still pockets of
moisture moving within the post-frontal flow. One such pocket is
currently moving over Molokai, while another is approaching
Kauai.
Winds will strengthen and shift out of the north then northeast
tonight as the surface high advances closer to the state. This
will keep moisture along the dissipating front focused over the
Big Island, initially along southeast slopes, then across north
facing slopes as the winds fill in. From Maui to Kauai, showers
will favor north facing slopes, with the greatest amount of shower
activity expected on Kauai.
Northeasterly winds will shift out of more typical trade wind
direction on Friday as the surface high passes north of the
state. The winds will likely be breezy and gusty over the western
end of the island chain, where a shallow band of moisture will
likely enhance windward rainfall. In addition, lingering moisture
from the stalled front should maintain wet conditions across
windward Big Island. A weak ridge aloft will produce rather stable
conditions.
Over the weekend, trade winds will become more easterly, perhaps
even out of the east-southeast near Kauai. The surface high will
move off to the northeast and settle midway between Hawaii and
California, with a trailing ridge moving to within a couple
hundred miles of Kauai. This will cause the trades to veer more
easterly and possibly lead to brief periods of weaker winds. A
weak disturbance aloft will pass overhead, but a mid level ridge
should hold, allowing modest rainfall to favor windward slopes.
Little change is due on Monday, though we could see trades drop
off and shift southeasterly late Tuesday or Wednesday as a front
approaches.
&&
.AVIATION...
Showers remain persistent in the Kau district of the Big Island
this afternoon as a weakening front stalls near the state. AIRMET
Sierra remains in effect from Cape Kumukahi to South Point.
Behind the front, scattered showers are pushing eastward down the
island chain. The movement of these showers has taken on a more
easterly trajectory from this morning`s northerly direction as
winds begin to shift around behind the front. There is a somewhat
organized line impacting Molokai as of 3 pm moving to the east at
about 10 kt. This has brought tempo MVFR conditions to PHMK, so
expect brief periods of MVFR with these heavier showers.
Light winds are continuing to switch around from the south to the
west and will eventually become more northerly by tonight across
the island chain. High pressure will continue to build to the
northwest of the state, which will bring the return of the trades
by Friday.
&&
.MARINE...
A dissipating front will linger around the Big Island into
tonight, then fade by Friday. High pressure will build north of
the state tonight and steadily move east through the weekend. This
will bring the return of strong trades, gradually veering from
the north towards east over the next several days. Currently, no
marine warnings are in effect, however, trade winds are expected
to increase to Small Craft Advisory speeds by Friday and likely
continue through the weekend.
Coastal flooding will remain possible over low lying areas for
the next couple of mornings due to higher than normal water levels
and large astronomical tides. However, subsequent high tides will
gradually lower heading into the weekend, with impacts decreasing
as well.
A series of small northwest swells will support small surf along
exposed shores through Friday. An upward trend this weekend could
support moderate surf by Sunday, but still below advisory level.
Guidance is still advertising a hurricane-force low developing east
of Japan this weekend which could translate to a very large northwest
swell arriving locally early next week. This swell will likely result
in warning level surf for north and west facing shores. A tiny, long-
period south swell will keep south shore surf from going flat this
weekend into next week. No other significant swells are expected.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Wroe
AVIATION...Dye
MARINE...TS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
531 PM CST Thu Dec 26 2019
.SHORT TERM...
145 PM CST
Through Friday night...
Anomalous warmth--record-breaking in fact for Boxing Day in a swath
from northern Illinois into Michigan--continues across the region,
although the winds of change are on the horizon here with the
approach of our next cold front. Temperatures early this afternoon
have soared into the low to mid 60s across much of the area,
although a sharp drop-off is occurring across far northwestern
Illinois with the arrival of low stratus and a northwest wind shift.
Moisture remains generally lacking downstairs ahead of the front,
although it does incrementally increase a tad with eastward extent
into portions of NW Indiana. As a result, have continued with a
precipitation-free forecast for the entire area with the main signal
for any light spotty showers or drizzle looking to remain
immediately off to the south and east of the CWA.
Guidance continues to generally struggle with the ongoing expansive
shield of low stratus in the post-frontal regime, with latest Day
Snow-Fog satellite RGB imagery showing this extends back essentially
across the entire state of North Dakota. Recent VAPOR aircraft
soundings out of Minneapolis-St. Paul reveal this post-frontal layer
remains saturated (or nearly saturated) to about 850 mb, which is
much deeper than most morning model guidance had indicated for this
afternoon. As a result, while the NAM has recently performed
abysmally in terms of low to near-surface moisture forecasts, have
generally followed it and the SREF this time around for the cloud
cover and high temperatures forecast for tomorrow (Friday) based on
upstream observations. In addition, an impressive subsidence
inversion looks to build in overhead which would further limit our
ability to vertically mix some drier air into the PBL. Could finally
see some chunks getting mixed out of the stratus deck towards late
Friday afternoon, but by this time it`d likely be too late for
temperatures to make much of a concerted rebound. Will show highs
for tomorrow mainly in the mid-upper 30s north of I-80, and in the
upper 30s to near 40 south with some potential that these still are
a hair too aggressive on the warm side.
Our attention will then turn to the system currently spiraling
across southern California at this hour which is slated to eject
across the Central Great Plains late Friday night. As is typical
with these anomalously deep and digging upper-lows, guidance
continues to incrementally slow the system`s forward progression,
such that there may be little in the way of precipitation through
Friday night/very early Saturday morning. That said, profiles do
appear to saturate just enough (up past 850 mb) by around daybreak
Saturday across the southwestern half of the CWA which should be
intercepted by a burgeoning wind of low-level warm advection. Looks
more like some spotty drizzle, so will keep the PoPs fairly low.
Temperatures may be flirting with the freezing mark across parts of
the I-39 corridor near Rockford, so can`t entirely discount a very
brief period of spotty light drizzle/freezing drizzle, but not
expecting anything in the way of notable impacts given the very warm
air immediately off the surface and already marginal surface
temperatures before things flip over to plain rain as temperatures
rise with the approach of a warm front.
Carlaw
&&
.LONG TERM...
211 PM CST
Saturday through Thursday...
By Saturday morning, an area of high pressure moving across the
region will shift east of the CWA to the Mid-Atlantic region as a
southern stream shortwave moves out of the southern Rockies with an
associated sfc low develops over the South High Plains, setting the
stage for the next significant chance for precipitation expected to
impact the area over the weekend.
The latest runs of the longer range guidance are trending toward
relatively consistent solutions, lifting the sfc low through the
Upper Missouri Valley Saturday afternoon/evening and then continuing
to the Upper Mississippi Valley Sunday morning. While the GFS/ECMWF
are trending to spreading pcpn into the wrn portions of the CWA by
early Saturday morning, and this is still a possibility, the models
are generally too fast in lifting southern stream shortwaves out of
the southern plains, so there is still a chance that the guidance
may still be a little fast, and that pcpn may not begin to
overspread the CWA until later in the day on Saturday than is
currently being advertised. However, as an extended period of warm,
moist advection sets up in advance of the system, still expect a
return of unseasonably high temps and dewpoints, with highs in the
lower 50s far north and upper 50s far south and dewpoints in the
lower 50s up to the I-80 corridor. With the increasing
temps/dewpoints, pcpn chances should ramp up quickly through the
afternoon and into the evening with the heaviest and steadiest rain
occurring overnight Saturday night. The GFS/ECMWF both show a little
instability, though with less favorable lapse rates, so will
continue the mention of slight chance tsra, though confidence in
anything more than isold/embedded ts over the wrn portions of the
CWA under modest upper level diffluence and stronger mid-level flow
of 60-75 kt.
A mid-level dry slot should move across the region Sunday as the sfc
cold front quickly pushes east and the main upper low wobbles around
the Upper Mississippi Valley before finally lifting newd on Monday.
Temperatures should remain unseasonably mild through Sunday
following the passage of the frontal boundary given the Pacific-
sourced air mass, with widespread temps in the upper 50s across the
area and a chance for temps to peg 60 F over the far southern
portions of the CWA. The true cold air will finally filter into the
region Monday night and Tuesday as the main upper system lifts to
the Upper Great Lakes, setting up deep layer cold advection.
Temperatures for early to middle next week should be closer to
seasonable levels with highs in the 30s and lows in the 20s.
&&
.CLIMATE...
The impressive stretch of winter warmth continues but will come to
an end today with the passage of a cold front. Rockford has seen
5 consecutive days with highs at or above 50F, which is now the
first time on record such a feat has occurred during the second
half December. For Chicago, it would be the first time since 1971!
Today`s record high temperatures have been broken at both Chicago
and Rockford.
&&
.AVIATION...
For the 00Z TAFs...
The concern for the aviation forecast is a likely period of IFR
cigs tonight, but low confidence on the duration and specific
timing.
A cold front has oozed through the Chicago area airports as of
23Z. Behind this front is a large area of low clouds extending
back through the Northern Plains. There is a narrow swath of IFR
clouds from western Illinois through north central Illinois. These
overlap with the cooling air and residual high low-level
moisture, favoring saturation of lower clouds and even MVFR
visibility. This regime should move into Chicago which is why we
continue the period of forecast IFR, and cannot rule out LIFR
ceilings either given there are several sites observing that to
the west.
Later into the night, the cold advection profile strengthens
slightly, and this typically results in cloud bases inching
upward. Given the time of day though, cannot rule out IFR
lingering into the morning rush though. Confidence on the
clearing time of MVFR clouds on Friday is low as well, but given
the satellite trends and observed moisture profiles upstream from
aircraft, we continue to favor it sticking around most of the
day. Otherwise winds will generally be westerly through tonight
and the day Friday.
MTF
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Blacksburg VA
1035 PM EST Thu Dec 26 2019
.SYNOPSIS...
High pressure will linger over the area through Saturday -
maintaining dry weather with above normal temperatures. Low
pressure will lift north through the central portion of the
nation Saturday night into Sunday night - bringing a widespread
wetting rain to the mid-Appalachian and mid-Atlantic region.
Drier weather, but with a continuation of above normal
temperatures will overspread the forecast area Monday into
Tuesday following the passage of a weakening cool front.
&&
.NEAR TERM /THROUGH FRIDAY/...
As of 1030 PM EST Thursday...
Satellite showed lower clouds across Kentucky and into Ohio
which will progress over the central Appalachians by morning
then across much of southwest Virginia, northwest North
Carolina and southeast West Virginia during the day.
Stratus was already forming in eastern Virginia and is expected
to spread west, reaching Buckingham to around Danville by
morning. Between the two areas with more cloud cover there may
be patchy fog overnight. Have may minor adjustments to overnight
lows with not much for cooling where the clouds will increase.
West of the Blue Ridge, some low clouds will develop early in
the morning and likely hang around for a portion Friday. This
will be associated with a weak shortwave that will struggle to
develop any precip at all with the dry airmass in place. Right
now, western Greenbrier tomorrow is the only place with any
meaningful pop were perhaps an isolated shower could occur.
Clouds tomorrow will limit some of our heating, keeping us
slightly cooler than what we will be this afternoon.
Forecast confidence is above average for today and tomorrow,
but drops to average or below for clouds/fog tonight and into
tomorrow.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 245 PM EST Thursday...
Weak short wave trof in northern stream will support the
southeastward push of a decaying cool front into the Blacksburg
forecast area on Friday night. However, passage of this front will
hardly be noticable, with only some mid-level clouds and the threat
of some evening sprinkles (more likely virga) most notably across
the SE WV mountains before axis of trof lifts north and east of
the area well before daybreak on Saturday.
Passage of weak front will be followed by weak ridge of surface high
pressure over New England that will wedge southwest into the mid-
Appalachian and mid-Atlantic states Saturday into Saturday night as
low pressure lifts northeast through the central plains into IA and
MN. However, absence of any cool advection, little to no post
frontal onshore flow, and a fair amount of insolation should erode
any low level inversion on southwest side of weak surface high
such that temperatures on Saturday should continue to be some
10-15F above seasonal normals.
Next threat of widespread rain is expected later Saturday night into
Sunday as isentropic lift ramps up through an increasingly saturated
H8-H6 layer with approach of western system. There may even be a
brief window where a rumble of thunder is heard as associated cool
front sweeps east through the forecast area on Sunday night;
however, mid-level atmospheric lapse rates are only barely
supportive of thunder, so not included in the forecast at the
present time.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 245 PM EST Thursday...
Following passage of the cool front, gradual clearing is
expected on/by Monday - especially in downsloping areas east of
the Blue Ridge and out across the Piedmont. Clearing may be
slowed somewhat across the west, most notably across the western
flanks of the Appalachains where some upsloping lingering
showers/sprinkles are possible through much of the day.
Flow aloft behind the departing system will remain zonal or
from the west-southwest, so any deeper cold air will again
remain mainly northwest of the Blacksburg forecast area such
that temperatures remain above seasonal normals through much of
the long-term period.
Post frontal weak surface high pressure system expected to maintain
dry and mild weather through Tuesday night before yet another
low pressure system lifts north through the Mississippi valley
Wednesday through Thursday. Moist isentropic lift in advance of
the system should increase the threat for another widespread
rain beginning as early as Wednesday afternoon - continuing
until a cool front on the backside of the system sweeps east
through the region on Thursday night.
As has been the case for much of the winter to date, cold air over
the mid-Appalachian and mid-Atlantic region will be absent such that
all precipitation will fall in the form of rain - with no threat
for any wintery weather until well after the New Year.
&&
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
As of 640 PM EST Thursday...
High pressure along the Atlantic coast seaboard is gradually
shifting eastward, gradually setting up some return flow with
moisture increasing through Friday. Expect VFR all sites early
tonight with some fog/stratus developing late. Confidence in
intensity and extent of fog/stratus is low with guidance of late
being a bit too aggressive and not verifying with extent of low
clouds currently visible on satellite. Believe the most likely
scenario is fog some valley fog west of the Blue Ridge affecting
both KLWB and KBCB, and low clouds/fog seeping in from the east
and southeast to affect KDAN and KLYH. Will go middle of the
road with cigs/vsbys and amend later as trends in satellite become
evident.
Any fog/stratus will dissipate Friday morning with VFR holding
on most locations, but MVFR cigs may develop west of the Blue
Ridge Friday afternoon at KLWB and KBLF with increasing low
level moisture.
Winds are expected to be light through the period with little
impact to aircraft operations.
Extended Aviation Discussion...
VFR weather conditions are expected through early Saturday. An
approaching front will bring increasing clouds and the threat
for rain Saturday night through Sunday night with widespread
sub- VFR likely. Monday should see return to VFR with gusty
winds. Exception should be lingering moisture of MVFR variety
across BLF/LWB.
&&
.CLIMATE...
As of 215 AM EST Thursday...
Another mild day, but records are not expected to be reached
for most of our climate sites, except possibly Blacksburg.
Thursday 12/26/2019
Site Record High/Year
Bluefield 68/1922
Danville 75/1982
Lynchburg 72/1922
Roanoke 70/1964
Blacksburg 64/1982
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
$$
SYNOPSIS...WERT
NEAR TERM...AMS/RR
SHORT TERM...WERT
LONG TERM...WERT
AVIATION...MBS/RR
CLIMATE...WP