Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/09/20

Area Forecast Discussion

National Weather Service Phoenix AZ

 430 PM MST Wed Apr 8 2020

.UPDATE...Aviation Discussion updated.

&&

.SYNOPSIS...
A slow moving storm system will mainly affect southern California
and western Arizona today bringing isolated to scattered showers
and thunderstorms. Very isolated showers and thunderstorms will be
possible into south central Arizona, with the best chances north
and west of the Phoenix metro. Cooler temperatures settle into
the region for Thursday and Friday with lower desert highs in the
upper 60s to lower 70s. Friday will also bring another chance for
showers and possibly a few thunderstorms mainly west and south of
Phoenix. The storm system finally exits the region on Saturday
with temperatures warming to just below normal readings by Sunday.

&&

.DISCUSSION...
Widespread showers associated with the leading edge of a weak
front and vorticity lobe rotating around a slow-moving cutoff low
occurred this morning in southeast California as expected. Rain
amounts were generally below a half inch with isolated totals up
to an inch aside from some radar-observed totals closer to 1.5
inches just east of Slab City near the Imperial Valley and in the
Yucca Valley just north of Joshua Tree National Park. Drier air is
beginning to filter in behind the front in southeast California
where isolated thunderstorms are attempting to form where skies
have cleared out. The best potential for showers and thunderstorms
appears to be in southeast Imperial and southwest Yuma Counties
based on model and observational trends. The Flash Flood Watch
remains in effect through 6 PM MST/PDT for all of southeast
California and the Colorado River Valley of La Paz and Yuma
Counties in case these storms continue to expand in coverage and
strengthen over the next few hours. However, these storms should
generally move fast enough to prevent significant flood issues and
are more likely to produce small hail and gusty winds.

Further east into the rest of La Paz and Yuma Counties along with
western Maricopa County, hi-res models have continued to trend
downwards with shower and thunderstorm potential. Aircraft
soundings into KPHX consistently show a capping inversion just
above 600 mb that will be difficult to overcome. However, weak
frontal forcing moving in from the west may be enough to generate
an isolated convective cell or two closer to the Phoenix metro,
with the best chances on the northern and western sides closer to
Surprise and Anthem. Otherwise, the main impacts this afternoon
for most of south central Arizona will be breezy southwesterly
winds producing 25-35 mph gusts in the Phoenix metro and isolated
stronger gusts further south and east. Gusts should quickly
subside later this evening, with winds generally staying below 15
mph except for far southwestern Imperial County in California.
Temperatures tonight will also be about 5-7 deg F cooler than last
night behind the weak front as skies clear.

Models continue to have a fairly good handle on the closed low
over southeast California slowing moving into southern Nevada
late tonight before retrograding to the southwest tomorrow night
back into southern California. This should generally keep the best
dynamics northwest of the region tomorrow to allow for most
locations to stay dry aside from western portions of Imperial and
Riverside Counties including Joshua Tree National Park. The
building mid-to-upper level ridge over the north central Pacific
centered just off the coast of Northern California should finally
kick out this cutoff low eastward along the southern Arizona and
California border with Mexico on Friday into Saturday. This should
trigger another round of isolated to scattered showers and
thunderstorms associated with this cold core feature on Friday
afternoon. The best rain chances on Friday will be over southeast
California and southwest Arizona with a median QPF ranging from
0.05-0.15", but with the upper end of guidance suggesting the
potential for 0.5-0.75". However, a slight northward shift in the
track of this low suggests our 20 percent PoPs for the Phoenix
metro may need to be adjusted upward in subsequent forecast
packages if this trend continues. Small hail and gusty winds will
be the primary threats with these fast-moving storms.

The closed low will be on its way out of the region on Saturday,
but it may linger across eastern portions of Arizona through
Saturday morning. Overall, Saturday should mostly be a dry day
with any rain chances confined to locations east and southeast of
Phoenix. After highs climb into the upper 60s to lower 70s across
the lower deserts on Thursday and Friday, temperatures will
increase into the mid to upper 70s for Saturday and lower 80s for
Sunday into early next week. Another shortwave disturbance will
move through Arizona on Monday bringing yet another chance of
lower elevation showers and high elevation snow to primarily
northern and eastern Arizona. Although the mid-to-upper level
ridge that will continue building off the West Coast into Alaska
appears to pushing a bit farther east in the operational GFS and
ECM models, there is broad agreement across both ensembles that
the ridge axis will likely be farther west. Thus, 20-30 PoPs
north and east of Phoenix with 10 PoPs for Phoenix seem reasonable
for now. Temperatures will warm a bit more and the region will
dry out next Tuesday as we remain under northwest flow between
the persistent ridge off to our west and trough to our northeast.

&&

.AVIATION...Updated at 2330Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Winds will continue to be breezy out of the west through the
evening (03Z or so) with SCT/BKN clouds around 5-6kft. Showers
will become a little more prevalent thereafter, but mainly focused
heading into the foothills north/east of Phoenix, along with
decreasing winds. Could see quite a bit of variability in cloud
cover through the night and across the metro area. Showers will
dissipate after 10Z or so, with clouds becoming more SCT for
Thursday. Winds will be considerably weaker.

Southeast California/Southwest Arizona including KIPL and KBLH:

Showers with a few storms pushing from southwest to the northeast
through the region now, a trend that will continue through 02-03Z
along with a weakening trend in their intensity. Thereafter,
clouds clearing up a bit with wind fields relaxing.

&&

.FIRE WEATHER...
Friday through Tuesday:
A low pressure system will linger over the region through Friday,
possibly even into early Saturday with chances for showers and
possibly a few thunderstorms on Friday across southeast California
and southwest Arizona. Cooler conditions will last through Friday
with desert highs mostly in the upper 60s to lower 70s. Weak high
pressure will overtake the region this weekend leading to drying
conditions and warmer temperatures, but still falling short of
normal readings through early next week. Min RH values between
30-40% are expected Friday before lowering through early next week
with readings settling below 20% by Monday. Winds will be
relatively light through the bulk of the period, but daytime
breeziness can be expected each day.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flash Flood Watch until 6 PM MST this evening for AZZ530-532.

CA...Flash Flood Watch until 6 PM PDT this evening for CAZ560>570.

&&

$$

DISCUSSION...Hopper/Kuhlman
AVIATION...Iniguez
FIRE WEATHER...Kuhlman




AREA FORECAST DISCUSSION

National Weather Service Raleigh NC

 915 PM EDT Wed Apr 8 2020

.SYNOPSIS...
A cold front will approach from the west late tonight, bringing
showers and storms through Thursday morning. The cold front will
cross the area Thursday, bringing strong gusty winds. Behind this
front, high pressure will bring cooler and drier air for late
Thursday night into Saturday. Rain chances return by Sunday and
Monday as another storm system moves in from the west.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 915 PM Wednesday...

What began as a couple of small storm clusters during the mid
afternoon over north central NC grew upscale in the hours since,
coalescing into a band of showers and strong storms which have
impacted central NC since 20z with high winds of 40-60 mph, a lot of
mostly small hail, and pockets of wind damage, feeding on steep low-
(~8.5 C/km) and mid- (~7.0-7.5 C/km) level lapse rates, moderate
MLCAPE near 1000 J/kg, and 40-50 kts of deep layer shear. This broad
broken band of showers and storms now extends across the far S
Piedmont across the Sandhills to the central/S Coastal Plain and
central Coastal Area. Outflows have largely raced out ahead of this
band but embedded discrete cells remain and will pose a continued
risk for small hail and 35+ kt wind gusts for another couple of
hours. A brief calm period will follow for much of the night with
fair to partly cloudy skies. Based on the latest CAM output and
extrapolation of upstream strong to severe convection over IN and
the Mid Miss Valley, it still appears that showers and storms are
likely to arrive in the NW CWA about 09z, crossing central NC over
the ensuing 4-5 hrs. Lows in the upper 50s to mid 60s. -GIH

Earlier discussion from 255 pm: We`ve been awaiting convective
initiation thus far, given the formidable cap around 800 mb and
dewpoints that are less than ideal, mostly in the 50s. But we`re
finally getting some agitated cu across the W Piedmont and Sandhills
where the CINH is finally dissolving and where dewpoints are
generally a bit higher than in the NE CWA, a function of the old
outflow generated from the early-morning MCS over OH/WV/VA. As
strong heating continues to chip away at the cap and culminate in
1000-1500 J/kg of MLCAPE within 30-40 kts of effective bulk shear,
we should see isolated to scattered convection develop over our far
N counties, developing further on its western flank as it propagates
to the ESE through early evening. Fat CAPE through the hail growth
zone aloft (a result of steep lapse rates through the EML, evident
in the 750-500 mb profiles in the 12z observed GSO sounding and in
proximity forecast soundings) still suggests a large hail threat,
with the wind profile indicative of possible splitting cells.
Damaging wind gusts remain a threat as well, with RAP downdraft CAPE
in the 800-1000 J/kg range. Once this activity exits the SE CWA,
likely in the late evening, we should see several hours of dry
weather and partly cloudy skies. Areas that happen to receive decent
rainfall later today could see patchy fog development, but the
presence of residual convective debris clouds to curb radiational
cooling may limit the fog threat, despite light winds. Our attention
then turns to what should be a band of strong to severe storms just
ahead of the approaching cold front over the Ohio Valley and Mid
Miss Valley tonight. Timing this convection (or its remnant MCV)
east-southeastward brings it into the western CWA toward daybreak,
so will trend pops up there very late tonight. Expect anomalously
warm lows in the upper 50s to mid 60s. -GIH

&&

.SHORT TERM /THURSDAY/...
As of 315 PM Wednesday...

...Wind advisory may be needed for Thursday...

The band of convection is expected to cross central NC during the
morning, departing the Coastal Plain around noon or shortly
thereafter. While there may be a few embedded strong storms, the
unfavorable time of day and waning large scale forcing for ascent
will reduce the threat of strong storms. The bigger story Thu may be
the strong winds from the W and WNW near and just behind the front,
with the potential to gust to 25-35 mph as strong winds at 925-850
mb are transported groundward. Will need to monitor high-res
guidance and morning observations to see if a short-fuse wind
advisory might be warranted. (See fire weather section below for
fire concerns.) Otherwise, expect fair skies with scattered flat
stratocu. Confidence in the high temp forecast is reduced by the
likely initial delay of the coolest air by the higher terrain, as it
appears that thicknesses won`t drop in earnest until well into the
afternoon. Will go with highs from the mid 70s in the NW to the mid
80s SE. -GIH

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
As of 200 PM Wednesday...

Thursday night through Saturday night: A large upper low will swing
through SE Canada and the Northeast US Thursday night. Meanwhile at
the surface, the cold front will continue pushing east of central
NC. Expect lows in the mid 40s NW to low 50s SE in the wake of the
fropa. Cold Canadian high pressure will build south into the Plains
Thursday night and shift eastward into and over the mid-Atlantic on
Friday/Friday night. Despite a shortwave aloft passing over the the
area on the back side of the departing upper low, expect the weather
to remain dry with NW flow and subsidence over the area. Expect
below normal temperatures Friday and Friday night with highs in the
upper 50s to mid 60s and lows in the upper 30s to low 40s.
Temperatures should moderate some to near normal on Saturday and
Saturday night as the surface high shifts east off the Atlantic
coast and weak sub-tropical ridging aloft builds over the Southeast
and mid-Atlantic. Highs in the mid 60s and lows in the mid 40s to
around 50 degrees.

Sunday through Tuesday: Little change in the forecast for the system
moving into the area Sunday/Monday. The upper low should be sampled
much better today, so expect model agreement to improve further in
the next day or so. This low will slowing make its way through the
Southwest by Saturday before getting caught in a deepening northern
stream trough and swinging east through the southern Plains, then
northeast through the MS Valley as a s/w trough Sunday/Sunday night.
The wave will then lift through the OH Valley and into the Great
Lakes and Northeast US Sunday night/Monday. At the surface, the low
will strengthen as the it moves east through the Plains and MS
Valley. The attendant cold front will push east Sunday night and
Monday, though specific details regarding the timing of the front
and the evolution/track of the low are still quite uncertain. Timing
for best rainfall chances is still between 12Z Sunday and 00Z
Tuesday. This system has the potential to result in some significant
rainfall amounts across central NC. Regardless, expect some
moderation in temperatures from Sunday to Monday and increasing
moisture and cloud cover as return flow off the Atlantic and
southerly flow from the Gulf ahead of the front advect warm, moist
air into the region. Given the uncertainty and dependence on the
timing and strength of the system, will not get into specifics
regarding temperatures at this time.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 845 PM Wednesday...

Storm clusters which impacted central NC since 20z with high winds,
a lot of mostly small hail, and pockets of wind damage have
congealed into a broad broken band of showers and storms, still
impacting FAY and RWI but has pushed well SE of INT/GSO/RDU. Aside
from the continued short-term storm threat at FAY, the other
terminals will remain largely dry with VFR conditions and much
lighter winds for much of the night. We`re likely to see areas of
fog, although given the overspreading mid and high clouds,
confidence in this occurrence is low. Another band of showers and
storms will cross central NC late tonight through Thu morning,
mainly 09z to 16z, and an hour or so of MVFR cigs/vsbys are possible
at all sites during that time. VFR conditions will return from W to
E between 13z and 16z. Attention will then turn to the strong gusty
winds from the W or WNW at sustained speeds of 15-20 kts and gusts
to 25-35 kts, dominating from late morning through the afternoon,
which could generate mechanical turbulence and present difficulties
in aircraft handling, particularly smaller aircraft.

Looking beyond 00z Fri, the strong and gusty winds should subside by
early Thu evening. VFR conditions will largely hold through early
Sun as high pressure builds over the area. A storm system will
approach from the SW from midday Sun through Sun night, bringing a
high chance of stormy sub-VFR conditions. Improvement is expected
Mon as the system exits to our E. -GIH

&&

.FIRE WEATHER...
Strong gusty winds from the W and NW are expected near and behind a
cold front that will cross central NC Thursday. These winds,
sustained at 15-20 mph with possible gusts to 25-35 mph, will occur
in conjunction with falling relative humidities, likely bottoming
out in the 25-32% range Thu afternoon as drier post-front air
spreads into the area. The combination of strong winds and low RH
will bring about concerns for adverse fire behavior, particularly in
areas that don`t see much rainfall either today or early Thu. Will
coordinate with forestry officials early Thu to address these
concerns. -GIH

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...Hartfield
SHORT TERM...Hartfield
LONG TERM...KC
AVIATION...Hartfield
FIRE WEATHER...Hartfield