Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/23/21
Area Forecast Discussion
National Weather Service La Crosse WI
1041 PM CDT Thu Apr 22 2021
.SHORT TERM...(This evening through Friday)
Issued at 202 PM CDT Thu Apr 22 2021
Forecast concerns will be elevated fire weather conditions in the
very short term, then increasing clouds with scattered showers
developing late tonight and into Friday.
Sunshine returned to the area today with temperatures warming
through the teens, 20s, and lower 30s into the 50s and lower 60s
by 2pm. Moisture in the 8k-10k level weak vorticity/warm advection
has produced a few clouds. More substantial clouds will develop
tonight as a shortwave over the Northern Plains will track east
into the region and weaken tonight and Friday. The moisture
transport vectors are more pronounced across the Southern Plains,
however an axis of moisture transport does extend northward into
Iowa and into the forecast area. Look for increasing mid and high
level clouds this evening with scattered showers developing Friday
morning. Some sprinkles may develop this evening with the leading
upper level jet support and mid-level warm air advection.
Scattered showers are progged mainly after 3am as the 35 to 40kt
low level jet over western Iowa lifts northeast into the forecast.
The showers appear more prevalent during the morning as the
shortwave tracks across the forecast area. Rainfall amounts are
expected to be mostly a tenth of an inch or less. isolated
activity in the afternoon. It will not be as cold with lows in the
30s and 40s tonight. Highs Friday should be in the 50s.
.LONG TERM...(Friday night through Thursday)
Issued at 202 PM CDT Thu Apr 22 2021
A front will move into the area then stall, with a stronger re-
enforcing front arriving Saturday morning. This will bring spotty
light rain chances to the area with winds turning to the
northwest and becoming brisk. Forecast soundings show the
potential for spotty instability showers Saturday afternoon as
well with the steep low level lapse rates and temperatures in the
40s and 50s. Surface high pressure will build in Saturday night.
850mb temperatures are forecast around -6 deg C in the thermal
trough and this combined with decreasing clouds should set the
stage for more freezing temperatures Sunday morning. Ridging
builds in Sunday, however a wave topping the ridge could bring
some shower chances with it. The much warmer temperatures do not
arrive until Monday, but when it does, we have highs in the 60s
and 70s.
The mid-level trough over the western U.S. gradually works east
Monday and into the Plains Tuesday. This system has a cold front
that moves into the region Monday, however the bulk of the
activity stays to our west until Tuesday through Wednesday.
Temperatures again Tuesday may approach 80 degrees with 70s
common. Showers and thunderstorms are expected with beneficial
rains of 0.5 to 1.5" possible. Not as warm Wednesday and Thursday
with highs in the 50s and 60s.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1040 PM CDT Thu Apr 22 2021
Mid-level clouds will continue to increase the rest of tonight,
but trends are for the low levels to remain quite dry well into
Friday morning. This trend continues to slow the expected
progression of rain chances into our area Friday morning and is
also keeping ceiling forecast a bit higher than earlier expected.
The RAP in particular is slower to moisten the low-levels than
other guidance, but it has a better handle on current cloud
trends within the moisture field upstream in the Plains. Have thus
delayed prevailing showers in the TAFs until mid morning at RST
and afternoon at LSE, but can`t entirely rule out a vicinity
shower or sprinkle at the TAF sites beforehand. Showers look to be
more hit or miss the remainder of the period as low level
moisture finally increases but with weak forcing. MVFR ceilings
are still likely to develop at both sites in the afternoon, but
IFR at RST is more questionable at this point. Winds will be out
of the south to southwest through the period, increasing by mid-
morning with some gusts around 20 knots in the afternoon, then
becoming light by evening.
&&
.FIRE WEATHER...
Issued at 202 PM CDT Thu Apr 22 2021
Elevated fire weather conditions continue this afternoon and
early this evening. The combination of low relative humidities
(20 to 30 percent) and west winds of 10 to 20 mph with gusts to
30 mph will allow fires to spread more easily. The winds will
decrease early this evening.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Kurz
FIRE WEATHER...Zapotocny
Area Forecast Discussion
National Weather Service Jackson MS
948 PM CDT Thu Apr 22 2021
.UPDATE...
Updated for evening discussion.
&&
.DISCUSSION...
Mid evening satellite imagery showed plenty of mid and high level
clouds to our west that will continue to thicken as they move
into our CWA tonight. The JAN sounding was rather dry and although
there are a few light returns on regional radar, measurable
rainfall will likely hold off in our western zones until after
sunrise. Temperatures were on track and no significant changes
were made to the current forecast. /22/
Prior discussion below:
This afternoon through Friday: Surface high pressure remains
entrenched over the ArkLaMiss region this afternoon while
increasing westerly flow aloft is bringing in abundant subtropical
moisture and increasing mid/high level cloudiness. There will
still be enough clear skies this evening to allow temperatures to
dip well into the 40s over eastern portions of the forecast area.
As a strong upper level shortwave trough moves from the southwest
CONUS into the Southern Plains Friday, quickly strengthening
moisture transport will help to initiate showers over western
portions of the area, especially by afternoon. /EC/
Tomorrow night through Saturday:
The forecast period will start off with an active round of weather
tomorrow night into Saturday. Guidance is in good agreement that a
shortwave trough ejecting out of the Desert Southwest will swing
through the Southern Plains tomorrow and through the Lower
Mississippi Valley tomorrow night. An associated surface low is
forecast to slide east along the Red River and through northern
Louisiana into northern Mississippi. This will bring a round of
thunderstorms, some of which could be severe, along with locally
heavy rainfall to portions of the area.
Severe weather threat:
A warm front will already be lifting north across southern
Mississippi at the start of the period tomorrow night. However,
return flow trajectories will be out of the southeast owing to a
sprawling surface high just off the Carolina Coast. Initially, this
will shunt rich boundary layer moisture and surface-based
instability further west into coastal Texas and southwest Louisiana.
As such, initial showers and thunderstorms along the advancing warm
front will be elevated above a surface stable layer. How far north
the warm front progresses remains uncertain, but the general
consensus is that it will reside in the vicinity of the I-20
corridor. Convective evolution has become more clear as 12z hi-res
CAM guidance is in fairly good agreement on warm advection showers
and storms breaking out during the evening hours followed by an MCS
sweeping through the area during the overnight. Guidance continues
to indicate a disjointed parameter space which remains the primary
limiting factor in higher severe weather probabilities at this time.
A stout 50-60kt low-level jet will support 500-600 m2/s2 of 0-1km
SRH and 40-50kts of 0-1km bulk shear, however, the aforementioned
southeasterly return flow will delay the arrival of surface-based
instability until winds can veer to out of the south/southwest. As
such, the severe weather threat will be conditional on the arrival
of surface-based instability prior to low-level winds becoming too
veered. Once flow veers, attention will shift to more of a flooding
threat as convection becomes outflow dominate and begins to train
within a shear profile characterized by nearly unidirectional west-
east flow oriented parallel to the warm frontal boundary.
With that being said, severe weather cannot be completely ruled out
within the highly sheared, yet very weakly unstable environment. The
HRRR and ARW solutions depict an MCS track north of I-20 with the
NSSL WRF along and south of I-20. In these events, the southerly
track tends to verify more often owing to the MCS propagating along
the instability corridor/gradient as well as cold pools from lead
warm advection storms helping to anchor the warm front further
south. If this scenario is realized, the slight risk along and south
of I-20 remains well placed with a threat for damaging winds and a
few tornadoes, as even a few hundred J/kg of SBCAPE will be
sufficient given the magnitude of shear present. If a further north
MCS track pans out and/or if surface-based instability is slow to
return there could still be a threat for severe weather, but it will
be more isolated and dependent on how deep the surface stable layer
is and whether stronger wind gusts can penetrate said layer.
Ultimately, it will come down to mesoscale trends tomorrow evening
as to how the event will play out, so will keep the ongoing marginal
and slight risk areas in the HWO as is.
While the vast majority of storms will shift east of the area
Saturday morning, there will be a secondary threat for storms during
the afternoon hours along the cold front/wind shift. Forcing will be
nebulous and deeper moisture will have already shifted out of the
area, but if a few isolated to scattered storms are able to initiate
the environment will remain favorable for severe weather. This will
mainly be in the form of large hail and damaging winds as moderate
instability and steep lapse rates will be in place with sufficient
deep-layer vertical wind shear for supercells. The NAM and GFS are
most aggressive with afternoon redevelopment and the timeframe is
currently outside of the window of the CAM guidance. Therefore, will
hold off on introducing another severe weather graphic for now, but
a marginal risk area may be needed if CAM guidance comes into
agreement on a few afternoon storms being able to develop.
Flash flooding threat:
PWATs are progged to surge into the 1.75" range with a stout low-
level jet aiding moisture transport into the aforementioned MCS.
Increasing ML/MU CAPE on the southwest flank of the departing MCS
along with veered boundary parallel flow will support a threat for
flash flooding from training convection. This will most likely occur
in a focused swath in the vicinity of the warm front where deep
moisture convergence is maximized, however, trying to pin down the
exact location remains elusive right now. The southern solution is
being favored, and while still somewhat broad, the elevated area in
the HWO/graphics has been focused mainly along and just south of the
I-20 corridor. Further refinement to the limited/elevated areas in
the HWO/graphics will likely be needed as placement of the heaviest
rainfall becomes clear and a flash flood watch may be necessary as
well.
Sunday through Tuesday:
Surface high pressure will quickly build in on Sunday with dry
conditions persisting as we head into the beginning of next work
week. A strong Pacific jet diving through California will help carve
out a stout trough with the synoptic pattern quickly amplifying.
This will allow for downstream ridging over the Lower Mississippi
Valley with rising heights and warming temperatures. Afternoon high
temperatures will quickly rebound into the low to mid 80s by Monday
and Tuesday beneath partly cloudy skies.
Wednesday through Friday:
The pattern will become increasingly amplified by mid to late week
as a strong Pacific jet diving down the West Coast helps carve out a
stout trough over the Desert Southwest. Guidance is in decent
agreement that this trough will eject into the Southern Plains on
Tuesday, but predictability starts to decrease by mid to late week
as it encounters upper ridging over the Lower Mississippi Valley.
The GFS solution is the most progressive and swings the system
through Wednesday night into Thursday. The ECWMF, however, quickly
slows the system as it encounters the aforementioned ridging and
shears out the wave with any active weather later Thursday into
Friday. Given the differences in guidance will keep the forecast in
line with the national model blend for now, but another round of
thunderstorms and heavy rainfall cannot be ruled out during the mid
to late week period. /TW/
&&
.AVIATION...
00Z TAF discussion:
VFR conditions and a light wind will prevail through Friday
morning. Coverage of -SHRA wl increase from the west Friday
afternoon and may result in brief vsby restrictions but VFR
conditions are expected to continue to prevail through the end of
the TAF period. /22/
&&
.PRELIMINARY POINT TEMPS/POPS...
Jackson 48 72 60 81 / 5 23 96 37
Meridian 45 72 58 80 / 3 10 98 56
Vicksburg 52 72 61 81 / 7 41 97 23
Hattiesburg 47 74 63 81 / 5 12 94 58
Natchez 52 74 62 82 / 6 47 96 22
Greenville 52 69 58 76 / 9 39 98 28
Greenwood 51 70 57 77 / 3 19 98 44
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.
&&
$$
TW/22/EC
Area Forecast Discussion
National Weather Service Norman OK
1057 PM CDT Thu Apr 22 2021
...New AVIATION...
.UPDATE...
Issued at 1251 PM CDT Thu Apr 22 2021
Latest radar loop depicts shower development occurring over
portions of northern Oklahoma. Based on latest radar trends and
high resolution guidance, increased POPs across northern OK for
this afternoon and evening, especially for areas near Ponca City
and Stillwater.
&&
.SHORT TERM...
(This evening through Friday)
Issued at 241 PM CDT Thu Apr 22 2021
Overcast skies are expected this evening through Friday, with some
clearing possible over the western zones tomorrow afternoon. There
remains quite a bit of uncertainty as to the prog`d surface low
and associated warm front and dry line tomorrow as the mid-level
trough ejects from Arizona early Friday morning. General model
consensus indicates the surface low develops over the TX panhandle
Friday morning and tracks southeast towards north TX. The HRRR
model has trended slower and farther north with the surface low
(from 06 to 12Z runs), which would place our area in the warm
sector longer with perhaps a more quickly eroding cap and higher
MLCAPE. This, however, tends to be the outlier. Areas of drizzle
appear likely beginning early Friday morning to midday over much
of the area and a strong cap will be in place.
There is the potential for scattered thunderstorms tracking
across north Texas and S/SE Oklahoma Friday morning into early
afternoon, some of which may be strong to marginally severe. Activity
that develops over north TX will affect the amount of low-level
moisture that reaches Oklahoma, and therefore, could affect storm
chances in the afternoon. CAMS suggest that supercells may develop
near the triple point Friday afternoon somewhere over our western
zones, depending on the track of the surface cyclone. Moderate to
strong instability appears likely over southwestern Oklahoma and
western north TX and sufficient bulk shear values should enable
developing storms to begin rotating rather quickly. Large hail,
damaging winds, and an isolated tornado appears possible. With
high PW values near 1.6 inches, there is also a marginal risk of
flash flooding for east- central Oklahoma.
Thompson
&&
.LONG TERM...
(Friday night through next Wednesday)
Issued at 303 PM CDT Thu Apr 22 2021
An upper ridge builds over the area over the weekend as Friday`s
storms system departs to the east. This will allow for a warming
trend with temperatures finally reaching above average Sunday after
our recent cool stretch. Winds will increase by Sunday as well as
lee cyclogenesis occurs east of the Rockies. This will likely lead
to a period of increased fire danger across western Oklahoma
and western north Texas Sunday through Tuesday.
Tuesday still looks to be a potentially active severe weather day
for at least the eastern half of the area, but many details still
need to be worked out in the model guidance. The GFS remains faster
with the trough and further east with the dryline, while the ECM is
slower with the trough and depicts a more impressive
instability/shear combo across much of the area. Trends will
continue to be monitored as we are still many days out from the
event.
The rest of next week looks fairly quiet after this system passes,
with temperatures returning to near normal and ridging building into
the region.
Ware
&&
.AVIATION...
(06Z TAFS)
Issued at 1038 PM CDT Thu Apr 22 2021
Mainly MVFR ceilings through much of the night before ceilings are
expected to drop into the IFR cat with some fog and drizzle
developing during the morning. LLWS will also occur at most TAF
sites overnight.
Some improvement in the ceilings may occur during the day, but
expected to remain MVFR with showers and thunderstorm chances
increasing late afternoon and continuing into the evening. A cold
front will also enter northwest Oklahoma and make its way toward
I-44 by the end of the forecast.
&&
.UPPER AIR...
Issued at 119 PM CDT Thu Apr 22 2021
An Upper Air flight is planned for tomorrow, April 23rd at 12Z and
tentatively tomorrow afternoon.
&&
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 50 67 50 70 / 20 80 70 0
Hobart OK 49 73 46 72 / 20 50 40 0
Wichita Falls TX 52 75 52 75 / 20 50 20 0
Gage OK 44 69 40 72 / 10 30 30 0
Ponca City OK 48 65 48 70 / 40 80 80 0
Durant OK 53 70 55 73 / 20 90 60 0
&&
.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&
$$
SHORT TERM...01
LONG TERM....08
AVIATION...30
Area Forecast Discussion
National Weather Service Las Vegas NV
843 PM PDT Fri Apr 23 2021
.SYNOPSIS...Can not rule out a light showers over Mohave County and
the lower Colorado River Valley this evening. A warm up still
expected for Friday through the weekend, but gusty southwest winds
return both Saturday and Sunday. Confidence is increasing for the
potential of widespread precipitation for the region as a large
Pacific System brings welcome moisture into the entire region by
early next week.
&&
.UPDATE...
A few showers continue this evening over eastern Mohave County with
even a thunderstorm east of Wikieup which should all exit over the
next couple of hours. The shortwave trough will push out of the area
overnight with a brief period of quiet weather on Friday as ridge
builds in. Expect dry, warm weather to end the work week with
weather changes on the way with wind for the weekend and increasing
precipitation chances early next week.
&&
.SHORT TERM...Tonight through Saturday.
Have seen 1 cloud flash associated with the earlier storm just north
of Searchlight. Current radar shows that cell has weakened as it
moved east into the Colorado River Valley around Lake Mohave.
Otherwise, HRRR continues to indicate at least a slight chance for
showers into this evening within the lower Colorado River Valley and
Mohave County.
Progressive pattern takes us into the weekend with return of gusty
winds. The trough axis will continue east across Arizona tonight
with a mid-level ridge poised to be over the area Friday. Ridge is
short-lived with models in good agreement showing a shortwave
ejecting inland across the Great Basin Saturday driving that
increase in southwest wind. Temperatures will warm through Saturday
with the potential for wind gusts approaching 40 mph.
.LONG TERM...Sunday through Thursday.
A large eastern Pacific low pressure system is forecast to move to
the west coast on Sunday and then inland across the western states
on Monday before exiting to the east on Tuesday with ridging
building in over the area on Wednesday.
Sunday is expected to be dry and windy area wide with headlines
potentially being needed to address strong winds and increasing fire
concerns.
Ensembles continue to forecast a large trough moving into the
western states on Monday bringing a widespread chance of showers to
our area. The system is forecast to remain progressive according to
the GEFS and is east of the area on Tuesday followed by ridging on
Wednesday. The EC ENS is less progressive and lingers the low over
the area into Tuesday before moving it east late Tuesday. It also
has ridging returning on Wednesday. Clusters appear to be evenly
split on the two solutions. The extended pattern will begin with
near seasonal temperatures on Sunday dropping to well below normal
Monday and Tuesday before returning to near normal by midweek.
&&
.FIRE WEATHER...Potential of strong winds and low humidity returns
this weekend, specifically to southeast Nevada and northwest
Arizona. With fuels critical or approaching critical thresholds a
Fire Weather Watch has been issued for both Saturday and Sunday. The
watch will be focused on the afternoon hours, as conditions will not
be as critical overnight as humidity values rise and winds weaken.
&&
.AVIATION...For McCarran... Southwesterly winds will be favored
through the evening hours with speeds of 8-10 knots and occasional
gusts to around 15 knots. Gusts will drop off overnight but light
southerly breezes will remain. Similar conditions expected Friday
with afternoon southwesterly winds gusting to near 20 knots. Skies
will be mostly clear.
For the rest of southern Nevada, northwest Arizona and southeast
California...Periods of west winds with gusts of 25-30 knots are
expected in the Western Mojave Desert near KDAG mainly in the
afternoon and evening today and Friday. Elsewhere, generally light
winds are expected through the TAF period, with more predominant
west or southwesterly winds in the afternoon hours. A stray shower
accompanied by gusty winds will remain possible through late
afternoon mainly across Northwest Arizona and far eastern San
Bernardino counties.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to
report any significant weather or impacts according to standard
operating procedures.
&&
$$
SHORT TERM/FIRE...Pierce
LONG TERM...Salmen
AVIATION...Outler
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