Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/07/19
Area Forecast Discussion
National Weather Service Denver/Boulder CO
914 PM MDT Fri Sep 6 2019
.UPDATE...
Issued at 914 PM MDT Fri Sep 6 2019
Scattered showers continue moving over Elbert and Lincoln Counties
with light to moderate rainfall. A few more showers are also
moving over Grand and Summit Counties. These should dissipate over
the next couple hours.
No changes to tomorrow`s forecast. The airmass should be drier, so
the threat of heavy rain will be diminished. Will still see
isolated to scattered showers in the afternoon. Temperatures will
be similar Friday`s highs.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 300 PM MDT Fri Sep 6 2019
The Stratus has dissipated across the plains at this time.
Convection is developed over the high country with one main
storm now over Jefferson County. Models show an upper trough,
mainly north of the CWA, to move east overnight and Saturday. The
upper ridge flattens as a result. The flow aloft is west-
southwesterly over night, then westerly on Saturday. There is
weak upward motion on the QG Omega fields for the CWA tonight,
then weak downward energy on Saturday. The low level winds should
be pretty normal drainage patterns overnight. On Saturday, they
are all over the place, but are generally weak upsloping by
afternoon. For moisture, the precipitable water values are in 0.75
to 1.35 inches this evening. By Saturday, they dry out somewhat
into the 0.50 to 1.00 inch range by Saturday afternoon. The dew
point temperatures are in the 50s to lower 60s this evening, then
they decrease into the 40s to lower 50s F by Saturday afternoon.
The latest Acars soundings show CAPE values around 1500 J/kg with
85/59 F. For pops, will go with 20-50%s this evening, a bit
linger overnight. On Saturday will drop pops somewhat across the
CWA. For temperatures, Saturday highs look to be 1-3 C warmer than
this afternoon`s highs.
.LONG TERM...(Saturday night through Friday)
Issued at 235 PM MDT Fri Sep 6 2019
A shortwave will pass north of Colorado Saturday night and Sunday
with the associated lift and front late in the day Sunday.
Low levels ahead of this trough will be fairly dry over most of
the area Saturday evening, with soundings showing DCAPE values of
1,500 J/kg which indicates the potential for downbursts across
the plains. Thunderstorms will dissipate as they move east
Saturday evening into the drier more stable air. Moisture will
increase Sunday as specific humidity levels will rise above 6.0
g/kg over the plains and precipitable water will reach 1.25
inches. Steady storm motion of at least 15 knots and the moving
upper level trough driving the convection will limit the duration
of storms and should keep the flooding threat low. However, a line
of organized storms could produce a period of heavy rain as it
passes.
A shortwave trough will then rotate around the upper level low
off the southwest Canadian coast, passing from the western U.S.
across Colorado near midweek.
On Monday drier air will move in from the southwest behind the
ridge. Tuesday through Thursday there will be a slight increase in
moisture leading to isolated storms Tuesday and a better chance of
storms on Wednesday and possibly Thursday across the forecast
area as the next trough approaches. A front is expected to move
through Thursday afternoon bringing gusty winds to 25 mph on the
northern plains. On Friday conditions will dry out again as a weak
ridge brings more westerly flow. There`s some discrepancy in
temperature forecasts this week, but highs should generally be in
the 80s on the plains. Some solutions would have us creeping back
into the 90s ahead of the midweek trough. It may cool into the 70s
behind the trough if this system connects well with the cooler air
to our north, but this varies from run to run.
Humidities will also be low with some wind behind the trough on
Monday, then it will still be dry with less wind on Tuesday. At
this time it does not look like widespread Red Flag conditions,
but we will be back to an environment where conditions are close
to the criteria in the afternoons, especially over the mountain
valleys.
&&
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 914 PM MDT Fri Sep 6 2019
No more aviation impacts overnight. Winds will remain out of the
south overnight. Drier air will move over the Denver area
Saturday, so coverage of showers will be much lower than earlier
today.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Dankers
SHORT TERM...RJK
LONG TERM....Sullivan/Gimmestad
AVIATION...Dankers
Area Forecast Discussion
National Weather Service Louisville KY
845 PM EDT Fri Sep 6 2019
.Forecast Update...
Issued at 845 PM EDT Fri Sep 6 2019
A cold front is draped across central and southern KY at this hour,
and will continue to work southward this evening. Seeing a few blips
on radar with good convergence ahead of the front, but have yet to
see any instances of actual rainfall, or even sprinkles for that
matter. The latest AMDAR soundings still show a healthy inversion
between H8-H7, and this should limit any deep convection in what
would otherwise be a pretty unstable environment. The blips on radar
are likely only to the depth of the inversion, and will not be able
to develop deeper. So, will remove thunder from the forecast, but
will keep the 20% chance of rain in the forecast for the next few
hours. Overall, the threat of measurable rain is quite low.
&&
.Short Term...(This evening through Saturday)
Updated at 253 PM EDT Fri Sep 6 2019
A well defined cold front is showing up on surface observations this
afternoon in central Illinois and Indiana. This cold front will
slide into southern Indiana over the next few hours, and eventually
central Kentucky this evening through the overnight hours. Models
continue to show the development of isolated showers and storms
ahead of the front, though they will have a strong cap to contend
with. Recent AMDAR soundings from SDF have shown ~16C temperatures
around 700mb, which would keep a lid on any convection... but model
soundings show this cap slowly eroding as the front approaches, so
it`s certainly plausible we could see an isolated shower or storm
late this afternoon and evening in central Kentucky. As a result,
will keep the mention of isolated PoPs in the forecast through the
early overnight hours.
The front should push through the region by midnight, leaving clear
skies temporarily in its wake. There`s a pretty good post-frontal
stratus signal for areas along and east of I-65 after 08-09z
tomorrow morning, and it looks like the stratus could persist for a
good portion of the morning and early afternoon hours. Some models
also show fog developing, but given that drier air will be advecting
in behind the front, and winds will remain light out of the north
through the early morning hours, fog formation seems unlikely unless
the stratus deck settles to the surface.
Temperatures will be on the cooler side tomorrow behind the front,
and may take a while to climb in areas that see extended cloud
cover. Forecast highs will generally be in the upper 70s to low 80s.
Dry conditions are expected.
.Long Term...(Saturday night through Friday)
Updated at 245 PM EDT Fri Sep 6 2019
Surface high over the Great Lakes will give us another pleasant day
on Sunday, with low dewpoints and seasonable temperatures. By Sunday
night a weak upper wave will pass to our north, and it appears the
sharpening warm front will be just far enough north to keep any
precip chances out of our area.
Upper ridge over the southeast CONUS will expand into the Ohio
Valley Mon-Tue, resulting in a warming trend. The hottest days will
be Tuesday and Wednesday, with highs in the lower-mid 90s thanks to
dry ground conditions. Dewpoints mainly in the mid/upper 60s will
keep heat indices below 100.
Ridge starts to break down late Wednesday, and more so Thu-Fri. Will
continue with slight chance afternoon/evening POPs each day and keep
temps above normal both day and night.
&&
.Aviation...(00Z TAF Issuance)
Updated at 751 PM EDT Fri Sep 6 2019
A cold front is pushing through the area at this evening, and is
bringing an increase in cloud cover, along with an outside chance at
a few isolated showers. Don`t have enough confidence that showers
will impact the TAF sites to include mention, but did want to focus
on the cloud cover in the short term, and in the early Saturday
morning hours. Ceilings should be clearing at the northern TAF sites
as of this writing, so will only mention Few around 3-4 K feet. BWG
will hold onto the ceilings for a few more hours before clearing.
Models are hinting at some fog toward dawn, but given steady N winds
and drier air behind the front, think we will hold off on mention of
fog, except at HNB were some brief MVFR vis is possible toward dawn.
The other concern is for some stratus clouds to build into LEX in
the pre-dawn hours and possibly SDF by mid morning. Will go ahead
and forecast below fuel-alternate and some IFR at LEX, but stay
optimistic at SDF between 14 and 18z. Otherwise, surface winds go
northerly with the frontal passage, and should stay some sort of NW
or N component through this forecast cycle.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...BJS
Short Term...DM
Long Term...RAS
Aviation...BJS
Area Forecast Discussion
National Weather Service Phoenix AZ
553 PM MST Fri Sep 6 2019
.UPDATE...
Updated Aviation section.
&&
.SYNOPSIS...
Seasonably hot weather will persist into the early part of the
weekend before a significant cool down into next week. A weather
system will move through the northern part of the region early
Sunday bringing rain chances to mainly eastern Arizona, but also
cooler conditions areawide. An unsettled weather pattern will
persist through the first half of next week with shower and
thunderstorm chances returning to much of Arizona while
temperatures fall to below normal readings.
&&
.DISCUSSION...
Mid-upper level ridge extends from the Baja Peninsula northeastward
into northern New Mexico, resulting in a light southwesterly
steering flow. Meanwhile, conditions are seasonably moist with PWATs
above 1.5 inches across the lower deserts. Latest ACARS soundings
indicate two warm layers around 850 mb and 450 mb, which is
resulting in considerable convective inhibition in the Phoenix area.
However, along the periphery of the Valley, MLCAPEs have
reached 500-1000 J/kg with less CIN. Latest local CAMs, HRRR and
HREF are in good agreement and indicate isolated thunderstorms are
likely in these areas, but will dissipate around sunset.
Mean layer flow will become more westerly Saturday ahead of a weak
short-wave trough across northwestern AZ and a deeper trough off the
CA coast. Latest National Blend shows slight warming ahead of these
systems, resulting in pockets of high Heat Risk across the Phoenix
area. The day will start out quite warm, possibly breaking the
record high min for the date of 87 degrees (set in 2011). Forecast
high in Phoenix is 108 degrees, though 110 degrees is not out of the
question. Latest long-range ensembles suggest this could also be the
hottest day for the remainder of the year and an Excessive Heat
Warning has been issued for the Phoenix area and Wickenburg. In
addition to the heat, drier air will overspread the southwestern
deserts, which will confine afternoon shower and thunderstorm
activity to Gila County.
&&
.PREVIOUS DISCUSSION...
Moisture levels still look to be on the increase beginning Saturday,
most likely Saturday night into Sunday as active monsoon conditions
across northern Mexico should send moisture northward into Arizona.
There is still some uncertainty for this weekend as any shift in the
track of the shortwave may change our rain/storm chances. Models are
at least in good agreement significant moisture will get pulled
northward ahead of the advancing trough, but mostly show the
moisture across eastern Arizona. The shallower depth of the trough
also means we will likely see more of a westerly dry flow aloft. For
now, best chances for rain fall across the eastern Arizona high
terrain early Saturday night through Sunday, with at least a chance
into the lower deserts later Sunday as a weak circulation across
Sonora Mexico inches northward near the border.
Model guidance diverges more for early next week with the
European ensemble suite pointing toward best rain chances for
south-central and eastern Arizona late Monday into early Tuesday
whereas the GEFS mostly distributes QPF evenly Sunday night
through Wednesday. Even though forecast confidence in the timing
and positioning of any subtle disturbances early next week is
quite low, it seems possible many locations from Phoenix eastward
should see at least some rainfall at some point Monday through
Wednesday. The potential storm severity and impacts look less
impressive now that the shortwaves are more likely to pass farther
to our north, but the increased winds aloft should at least keep
a chance of some strong storms in the forecast early next week.
Anticipated QPF amounts are just as hard to pin point, but with
forecast low level mixing ratios near 12 g/kg this will at least
bring some localized flooding potential across the eastern half of
Arizona.
As our long lasting high pressure ridge finally gives way to
broad scale upper level troughing beginning Sunday, much cooler
air will settle across the region. Forecast highs drop to between
100-105 on Sunday and bottom out in the middle 90s to around 100
degrees for Tuesday and Wednesday. Unfortunately, models agree the
high pressure ridge will begin rebuilding late next week,
eventually becoming centered over the Southwestern U.S. at some
point the following weekend. The increasing heights aloft and
drying conditions late next week will bring temperatures back to
around or even a few degrees above normal at some point late next
week.
&&
.AVIATION...Updated at 0055Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
An isolated storm over northern portions of the metro (near/north
of 101 Freeway) passing through the vicinity of DVT will cause
enhanced gustiness for a brief time though it appears that it will
dissipate before reaching SDL. Expect storms to remain outside of
the vicinity of PHX and IWA. Couldn`t rule out outflow reaching
PHX and causing a change to a crosswind but confidence in that is
too low at this time to reflect in the TAF. Will continue to
monitor. Otherwise, expect storms in the region to taper off with
decreasing surface heating. Overall, westerly winds will prevail
the rest of the evening with a slow trend toward
downvalley/drainage patterns. Expect PHX will be the last of the
TAF sites to lose the west wind tonight before light and variable
toward morning. Also toward morning, anticipate isolated weak
showers to pass by to the east possibly brushing IWA. Otherwise,
anticipate the development of ceilings (bases AOA FL120) roughly
between 10Z-16Z. Saturday`s storm activity is anticipated to
remain well east of metro Phoenix. Anticipate a bit stronger
southwest and west winds in the afternoon as well.
Southeast California/Southwest Arizona including KIPL and KBLH:
No pressing aviation concerns for the TAF sites though IPL is
expected to have a modest sundowner this evening with a distinct
change to westerly winds with some moderate gustiness early this
evening. Expect west winds to continue at IPL through the period
with some gustiness developing again Saturday in the afternoon.
Meanwhile BLH will follow familiar diurnal trends with more
noticeable gustiness Saturday afternoon.
Aviation Discussion not updated for amended TAFs.
&&
.FIRE WEATHER...
Monday through Friday:
Isolated to scattered showers and thunderstorms will continue each
day on and off from Monday into Wednesday, especially from the S-
central lower deserts to the higher terrain of east AZ. Max Ts
will stay several degrees below seasonal normals through Thursday.
Min RH will range from the teens over SE CA to above 20 percent
elsewhere through Thursday before drying to the teens on Friday.
Excellent overnight recovery through Tuesday night will fall to
fair by Friday night. Winds will be light to seasonably breezy.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM to 8 PM MST Saturday for
AZZ534-537-540>544-546-548>551.
CA...None.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...AJ
FIRE WEATHER...Sawtelle