Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/23/20
Area Forecast Discussion
National Weather Service Cheyenne WY
743 PM MDT Wed Jul 22 2020
.UPDATE...
Issued at 737 PM MDT Wed Jul 22 2020
Areas of heavy rainfall have developed across the south Laramie
Range and to its east. A small stream flood advisory will remain
in effect through 9:45 pm tonight in northwest Laramie County to
cover the flood threat due to the large amount of radar estimated
rainfall being observed. Lighter rainfall has been noted further
north and west. Rainfall and thunderstorms should continue to
about midnight until a shortwave embedded within a southwesterly
flow aloft finally passes. A quiet night is in store for the
remainder of the night, with fog possible where the heavy rainfall
occurred and have made this adjustment to the forecast.
&&
.SHORT TERM...(late this afternoon through Thursday)
Issued at 200 PM MDT Wed Jul 22 2020
Compared to this time yesterday, convection early this afternoon
was limited to scattered CU forming over the higher terrain.
HRRR/RAP soundings revealed a capping inversion around 700mb, with
upwards of -300 surface- based convective inhibition. The 18Z
HRRR progs isolated thunderstorms developing along the I-25
corridor by 22Z, with a greater coverage of convection spreading
northeast from western and central CO into south central WY after
00Z. Despite SBCAPEs of 2000-3000 j/kg east of the Laramie Range,
around 25 kt 0-6 km shear will result in a few strong storms
capable of gusty outflow winds and possibly small hail. Most
shower/thunderstorm activity will wane later this evening, with
isolated elevated convection possible over the northeast plains
late tonight and early Thursday morning.
Isolated to scattered afternoon convection develops across the
southern 2/3 of the CWA Thursday. SBCAPEs are progged from 500-1000
j/kg range with weak 0-6 km shear. Severe threat will be low, with
isolated strong storms with gusty winds and small hail possible.
It will be warm with highs in the 70s and 80s west of I-25, and
90s to the east.
.LONG TERM...(Thursday night through Tuesday)
Issued at 311 AM MDT Wed Jul 22 2020
Upper level ridge will continue to persist over the intermountain
west for the medium range to long range forecast. Split flow due to
a weak upper level low at the the base of a shortwave trough Friday
night into Saturday will help with a monsoon moisture plume surge
toward the Central Rocky Mountains/Front Range/Laramie Range. 700mb
temps on model guidance show pockets of lower temperatures in the 8C-
12C range most likely due to cold pooling associated with convective
cell migration to the north and northeast overnight into Saturday
morning. Diurnal heating coupled with modest low level southwest
airflow from the 4 corners region will advect warm air into the
region. Would not be surprised to see high temperatures crest 90-100
degrees east of the Laramie Range for Saturday. Continued surges of
monsoon moisture and afternoon convection look to limit afternoon
highs for Sunday, Monday, and Tuesday despite atmospheric ridging
present in the upper levels. Overall, a fairly active weather pattern
is favored for the extended period with above average temperatures
for the CWA as well.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 509 PM MDT Wed Jul 22 2020
A few showers and storms over far se Wy this evening with vcts
affecting KLAR. Other showers may move north out of Colorado for a
time this evening as well. Otherwise VFR expected to prevail with
monsoonal moisture resulting in fairly widespread mid and high
clouds over the area through Thursday.
&&
.FIRE WEATHER...
Issued at 123 PM MDT Wed Jul 22 2020
A ridge of high pressure aloft will be situated over the central and
southern Great Plains for the next several days. Clockwise flow
around the ridge will draw monsoonal moisture from the Four Corners
into the bi-state region. Instability combined with weak upper level
disturbances will produce isolated to scattered mainly afternoon and
evening showers and thunderstorms. Winds will be light to moderate,
except variable and gusty near thunderstorms.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
UPDATE...AB
SHORT TERM...MAJ
LONG TERM...BMW
AVIATION...RE
FIRE WEATHER...MAJ
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1056 PM CDT Wed Jul 22 2020
.UPDATE...
Issued at 940 PM CDT Wed Jul 22 2020
Have made some minor modifications to the forecast tonight. Have
raised forecast lows across eastern South Dakota. With increasing
winds, temperatures should struggle to cool substantially. In
addition, have delayed pops till closer to 09Z when low level warm
air advection increases.
&&
.SHORT TERM...(This Evening through Thursday)
Issued at 317 PM CDT Wed Jul 22 2020
The primary concern in the short-term is convection chances for
tonight into Thursday morning. Convection over the forecast area
has momentarily ended. Satellite shows some flat cumulus over
Tripp county and will continue to watch that area for development.
However, model soundings show a strong enough cap exists (~ -50
J/kg) to prevent convection from developing. We did keep a slight
chance of thunderstorms into the evening in south central SD should
cumulus break the cap. Of more significance is a combination of a
weak upper level wave that will move along the SD/NE border
overnight combined with strong WAA between 850 and 700 mb ahead of
a developing cap. Model soundings show that parcels based between
800 and 700 mb only have a very weak cap by 09Z. Expect that lift
along the mid level boundary, which will be on the nose of the
LLJ, will result in convection developing between KYKN and KSUX -
likely near the Missouri River - after 06Z. CAMs have been split
on how widespread development will be. THe latest HRRR shows
isolated convection with a few light showers while the ARW and NMM
show significant convection from KFSD into much of eastern
Nebraska. While MUCAPEs are 1000-1500 J/kg, am more uncertain if
the cap will be as weak as shown by model soundings and that could
limit coverage of convection later tonight into Thursday morning.
So kept PoPs in the 30-50 percent range. Severe weather is not
expected given effective shear of 20 kts or less but initial
updrafts may be able to produce up to dime size hail later
tonight. As the LLJ weakens Thursday morning, convection should
rapidly diminish and is unlikely to make it as far east as Storm
Lake.
As for temperatures, high pressure will slowly move east
overnight. Winds will remain in the 5-15 mph range west of I-29
and with increasing moisture, lows will remain in the upper 60s.
Near Hwy 71 in Iowa and Minnesota, lighter winds and clear skies
will allow lows to fall to around 60 degrees. On Thursday, south
winds will continue to increase bringing warmer air northward.
Highs west of I-29 will reach the lower 90s with mid to upper 80s
elsewhere. With dew points at or above 70 by the afternoon, places
in the James Valley could see heat indices reach 100. Given
forecast heat indices are at or just above 100 for an hour or two
decided to hold off on any heat advisory in case dew points do not
warm as quickly as forecast.
.LONG TERM...(Thursday Night through Wednesday)
Issued at 317 PM CDT Wed Jul 22 2020
The heat and humidity will continue into the weekend.
On Thursday night, all deterministic models now show a strong cap
in place over the forecast area with convection staying to the
west and north of the area where a boundary will be in place and
the upper level wave tracks. Therefore have removed PoPs from the
forecast from Thursday afternoon into Thursday night. With high
dew points moving into the area, lows will be in the 70s.
Friday and Saturday will be hot and humid across the area. Both
days will see highs well into the 90s and, with dew points
remaining from 70-75, heat indices in much of southeastern South
Dakota into northwestern Iowa and northeastern Nebraska will be
from 100 to 105 degrees. With temperatures closer to 90 in
southwestern Minnesota, the forecast heat indices are from 95 to
100. However, like last weekend, it is possible dew points on one
or both days could be 2 to 4 degrees higher which would likely
result in heat indices closer to what was seen last weekend.
Regardless, dangerous heat will be over the area so those planning
outdoor activities on either Friday or Saturday should be
prepared.
The other question is convective possibilities. All models keep
the front north and west of the area through Saturday afternoon.
So convective initiation will be to the north and west of the
area during the late afternoon on Friday. The question will be if
storms can develop/propagate far enough southeast to impact the
forecast area. On Friday night, storm motion will be northeast to
east-northeast. This track should keep most storms out of the
forecast area with the best chance from north of Chamberlain to
Marshall Minnesota. On Saturday afternoon evening, the front
will be moving toward Highway 14. This means convection is more
likely to either develop or move into the area from late afternoon
into the evening. MLCAPEs will be over 3000 J/kg and effective
shear will be around 30 kts so there will be the potential for
isolated severe storms Saturday afternoon and evening.
Temperatures will return to normal Sunday and into early next
week.
&&
.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1053 PM CDT Wed Jul 22 2020
VFR conditions through 08Z Thursday. Thereafter, expect elevated
storms to develop south of highway 18 impacting the Yankton area,
and spreading northeast through the morning. Have a period around
sunrise where the I-29 corridor will be impacted south of FSD.
Expect cumulus field to develop during the day on Thursday, with
gusty southeast winds.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&
$$
UPDATE...BT
SHORT TERM...Schumacher
LONG TERM...Schumacher
AVIATION...BT
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
636 PM CDT Wed Jul 22 2020
.SHORT TERM...(This evening through Thursday)
Issued at 321 PM CDT Wed Jul 22 2020
A well defined MCV moved through central Nebraska this morning. This
brought a few showers and non-severe storms to the area. This has
now moved out of the forecast area and become a little more
diffuse. The main question today has been how much of a severe
threat we end up having the rest of today.
The severe threat is certainly looking less impressive for this
evening, but there is at least still a conditional risk for a strong
to marginally severe storm or two. The HRRR and RAP have been very
adamant that no convection will develop behind the remnant MCV, but
the NAMnest and NSSL WRF show a few scattered storms developing near
warm front in southwestern portions of the area. I tend to favor the
more conservative HRRR/RAP solution, as they are handling the MCV
very well, but cannot totally rule out something developing. IF
storms do develop, CAPE and shear are supportive of severe
updrafts producing large hail and damaging wind.
Later tonight, additional scattered showers and storms are expected
to develop on the nose of an increasing low-level jet. The location
of the jet would favor northeastern third of the forecast area.
Severe storms appear unlikely at this point.
Thursday is expected to be a dry and warmer day as we see rising
heights aloft and increasing southerly flow near the surface.
Highs are forecast to reach the low to mid 90s with southerly wind
gusts of 25-30 MPH.
.LONG TERM...(Thursday night through Wednesday)
Issued at 321 PM CDT Wed Jul 22 2020
The warming trend continues on Friday. Although we will likely
remain below advisory criteria, the humidity will push heat index
values to around 100 degrees for many locations. Slight chances for
thunderstorms creep into northwestern portions of the area overnight
along with the next approaching trough and surface front. That said,
this will likely remain primarily over the panhandle and western
Sandhills.
Saturday is still expected to the hottest day of the forecast
period, and heat index values may approach 105 degrees in some
spots. There is another chance for thunderstorms during the evening
and overnight as the next trough continues to edge closer, but we
still anticipate most of the local area to remain dry.
Temperatures are a little more uncertain on Sunday, as a cold front
is forecast to push into the area. Some locations will still
likely push into the mid 90s ahead of it, though. This front will
also likely bring us thunderstorms by the late afternoon and
evening. Convective details remain pretty uncertain in day 5, but
relatively high precipitable water and instability could lead to a
few severe storms or flooding issues through Sunday night.
Good chances for thunderstorms continue on Monday, but this will
depend heavily on how far south the front pushes or if it stalls out
in the local area. Regardless, temperatures should be around 10
degrees cooler than on Saturday. Slight PoPs continue Tuesday
and Wednesday, but confidence is not high at this point. The
latest ECMWF shows a drying trend, but the GFS does not have as
much of a dry push behind the front, and therefore lingers
precipitation in or near the area through this period.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday)
Issued at 635 PM CDT Wed Jul 22 2020
Significant wx: Low level wind shear (LLWS)
Tonight: VFR. Few lingering CU should dissipate around sunset.
Have removed the VCTS through the early eve as subsidence behind
departing MCV looks to quell tstm activity. However, later
tonight, an incr LLJ could bring tstm chcs to near GRI, but esp
points N and NE. It will also cause LLWS, esp. at EAR, through
around dawn. Any convection that develops will be elevated, so
only mid to high clds expected. Confidence: Medium to high.
Thu: VFR. Fairly quiet conditions expected, with only issue being
incr sfc winds out of the SE-SSE. Sustained winds will incr to
15-17kt, with gusts 24-26kt for the aftn. May see a few aftn CU
with bases 3-4K ft. Confidence; High.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
SHORT TERM...Mangels
LONG TERM...Mangels
AVIATION...Thies
Area Forecast Discussion
National Weather Service Goodland KS
546 PM MDT Wed Jul 22 2020
.SHORT TERM...(This evening through Thursday night)
Issued at 159 PM MDT Wed Jul 22 2020
500 mb RAP analysis and satellite imagery showed an upper ridge
building across the Rockies early this afternoon, with weak
northwest flow over the region. An MCV from last night`s convection
continued east along the Kansas/Nebraska border. Skies were sunny,
with some high clouds moving in from the west as thunderstorms
developed along the Front Range. At 2:00 PM MT, temperatures were
in the upper 80s to mid 90s, with southerly winds gusting at 25
to 35 mph for the central portion of the area. A field of cumulus
clouds was developing west of St. Francis.
A few thunderstorms are forecast to develop over the northern
half of the region this afternoon and evening where boundaries
remain from this morning`s convection. However, confidence in
storms forming/maintaining is low at this time. If thunderstorms
are able to kick off, instability, shear, and hodographs suggest
that a severe storm or two can develop with all modes of severe
weather possible. Even a tornado cannot be ruled out. The best
chance for severe weather will be along and north of Interstate
70. Thunderstorm activity should come to an end across the region
by midnight MDT, as temperatures fall into the 60s and low 70s.
The upper ridge moves onto the Plains on Thursday with an upper
trough to its west, placing the region under southwest flow aloft.
Breezy south winds are expected once again, with mostly/partly sunny
skies and highs in the 90s. As moisture filters into the region from
the southwest, thunderstorms may develop in the late afternoon and
continue into the evening hours, mainly for locations along and west
of Highway 27. At this time, severe weather is not expected.
Temperatures fall back into the 60s and low 70s Thursday night, with
dry conditions returning to the area by midnight.
.LONG TERM...(Friday through Wednesday)
Issued at 108 PM MDT Wed Jul 22 2020
For the start of the extended period not much has changed. Models
are still showing the local area under the influence of a strong
upper-level high and ridge over the Plains that is producing weak
southwesterly flow aloft over the Central High Plains region. This
pattern will produce above normal temperatures (middle 90s) and a
daily chances for showers and thunderstorms through the weekend.
For the start of next work week, the high will move more
southwestward, towards the desert southwest, allowing for a low
pressure system, and its associated front to transit south over the
Great Lakes and northern High Plains regions. As of now, the models
do show this front reaching the central High Plains region by
Monday. If this holds, the local area will see an increase chance of
showers and thunderstorms and closer to normal temperatures through
the middle of next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 523 PM MDT Wed Jul 22 2020
VFR conditions are expected at MCK and GLD through the 00Z TAF
period. Gusty south southeast winds will lose some gustiness after
sunset with some low level wind shear developing at both locations
after 04Z that continues through about 11Z before dissipating
around sunrise. South winds will become gusty again by mid day on
Thursday with scattered high clouds remaining across the area.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
SHORT TERM...JBH
LONG TERM...BW
AVIATION...LOCKHART
AREA FORECAST DISCUSSION
National Weather Service Morristown TN
903 PM EDT Wed Jul 22 2020
.UPDATE...
EVENING UPDATE.
&&
.DISCUSSION...
Still a few storms across the area as the sun is setting. Coverage
is beginning to decrease but some of these clusters of storms
looks to still be capable of producing new storms from their
outflow, especially in the Tri Cities are and near the NC/TN/GA
border. Expect storms currently on radar to somewhat persist for a
while, but overall the coverage of storms this evening should
remain relatively low. Will continue with low end PoPs across most
of the area with increased chances where there is currently storms
on radar. Overall only a few tweaks to the forecast in the evening
hours, otherwise everything else remains on track.
ABM
&&
.AVIATION...
00Z TAF DISCUSSION.
Storms should continue through the rest of the evening and
begin to decrease in coverage with the setting sun. If a storm
does impact an airport it would likely only last briefly with
strong winds and heavy rain being the main hazards. Fog is not
expected overnight unless an airport receives heavy rain...And we
can expect more summertime thunderstorms once again tomorrow
afternoon.
ABM
&&
.PREV DISCUSSION...
/ISSUED 334 PM EDT Wed Jul 22 2020/
SHORT TERM...(Tonight and Thursday)
Key Messages:
1. Scattered thunderstorms through this evening capable of producing
locally heavy rain, with less of a chance for isolated strong winds.
2. Marginal risk for severe thunderstorms and excessive rainfall
Thursday with widespread thunderstorms expected to develop. The main
impact will be localized flooding and strong winds.
Discussion:
This afternoon/evening...
Latest water vapor and RAP analysis shows a strong shortwave
progressing across the lower Great Lakes and OH Valley with a
surface low near the thumb of MI extending a cold front from NW OH
through central MO. This system will continue moving eastward the
rest of the day further breaking down the persist SE U.S. ridge as
the surface high retreats to the E. Much of the dynamics are across
the eastern Great Lakes and NE U.S. associated with a 60-80 kt 300
mb jet, but some confluence aloft, lowering heights with cooling mid
level temps, and low-level moisture and instability have resulted in
numerous diurnally driven thunderstorms this afternoon. Much of the
activity is over the plateau and eastern mountains as of 18Z, but
this will fill in across the valley late this afternoon through the
evening, so maintained chance to likely PoPs with the highest values
over the higher terrain. The threat of severe weather has decreased.
MLCAPEs are 1000-1500 J/Kg, but DCAPEs are only 400-500 J/Kg, and
when combined with 0-6 Km shear generally under 10 kts, any strong
downdrafts will be isolated. Localized flooding continues to be the
main concern with 1.8 to 2.10 inch PWATs, and weak wind field
leading to very slow storm motions. One hour Flash flood guidance is
only around 1 inch across the N Plateau and NE TN and parts of SW
VA, so these areas will be most susceptible.
Tonight...
The initial shortwave will progress into the NE U.S. with the
associated cold front making its way south and eastward toward the
lower OH Valley. Since the forcing remains N through the night,
believe most of our convection will dissipate after 02 or 03Z as the
boundary layer cools, but still kept slight chance PoPs across
northern areas through the night closer to the slowly approaching
boundary. Lows will remain mild in the upper 60`s/low 70`s.
Thursday...
A secondary shortwave looks to dive into the NE U.S. setting up a
slightly cooler and drier NW flow pattern over the eastern CONUS,
which will finally drive the cold front through the S Appalachians
as Canadian high pressure builds across the Great Lakes. This
frontal boundary will cross slowly and not clear to our S until Fri
morning. Looking at the forecast details, an active day of diurnal
convection is expected due to a subtle increase in wind energy aloft
on the periphery of this trough and associated jet dynamics combined
with increasing convergence ahead of the front. Forecast soundings
show a very weak cap around 700 mb during the morning, but this will
quickly break as convective temps are reached by late morning. There
will be a few stray showers early in the morning, but expect most
convection to develop after 15Z starting across northern areas, as
well as the plateau and eastern mountains, then expanding through
the afternoon. CAMS suggest this timing and location which increases
confidence, so have chance PoPs in the morning increasing to
likely/categorical during the afternoon. Severe chances are a bit
better owing to the SPC marginal risk areawide. Shear in the 0-6 Km
layer increases to around 20 kts by evening across the north half of
the CWA with MLCAPE projected at 1000-2000 J/Kg, LI`s of -5 to -8,
and low-level lapse rates above 7 C/Km, although DCAPE remains low
at 500-800 J/Kg. The improved shear with these at least modest
thermodynamics favors some multicell clusters and faster storm
movement leading to potential areas of wind damage. Wet bulb zero
heights generally over 13,000 ft will continue to limit hail
potential. Additionally, most of the area is under a marginal risk
for excessive rainfall. Just like today, this will be the biggest
threat with PWATs in excess of 2 inches (90th percentile) and fairly
warm cloud depths supporting efficient rainfall. As mentioned, storm
motions will be faster keeping the flooding threat localized, but
areas of training will need to be monitored, especially where heavy
rain has occurred the past couple of days. Highs will generally
range from the upper 80`s/low 90`s.
Garuckas
LONG TERM...(Thursday Night through Wednesday)
The main story during the extended continues to be the oppressive
heat and primarily diurnal thunderstorms.
Model guidance indicates a subtle shortwave tracking SE across the
forecast area on Thursday night and Friday morning. This will result
in higher PoPs and chances of some rain and thunderstorms. With
models indicating PW of around 2.0 inches, locally heavy downpours
will be likely producing a risk of localized flash flooding in
flashy areas and locations that have already received heavy rain
this week. Believe the severe risk will be very low on Friday
afternoon with the shortwave axis forecast to be moving east of the
forecast area by Friday afternoon. Isolated damaging microburst
winds will continue to be possible with the strongest storms.
Subsidence behind the departing shortwave is expected to be more
pronounced on Saturday bringing lower PoPs to most of our forecast
area. Highest PoPs on Saturday will be across the southern and
southwestern counties near a weak boundary around the periphery of
the ridge. With upper ridging bringing 591 to 593hpa 500mb heights
to the area through early next week, only isolated pulse convection
is anticipate late weekend through early next week. Above normal
temperatures and heat indices of 100 to 105 will be probable for
many locations.
The GFS and ECMWF both indicate a shortwave tracking eastward across
the Great Lakes next Tuesday with an associated surface low and
frontal boundary. Larger differences exist mid-week. The GFS takes
the trough axis eastward and builds in strong ridging across the
Gulf Coast while the ECMWF weakens the ridge and results in longwave
troughing across the Appalachians. While this adds to uncertainty
next week, a general increase in convection as heights lower and the
front approaches is forecast for Tuesday and Wednesday.
JB
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 74 93 73 92 73 / 40 50 20 60 20
Knoxville McGhee Tyson Airport, TN 73 91 72 90 71 / 30 70 30 60 20
Oak Ridge, TN 72 91 71 91 70 / 40 60 30 60 20
Tri Cities Airport, TN 69 88 68 86 67 / 30 70 40 60 20
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
520 PM MST Wed Jul 22 2020
.UPDATE...Updated aviation discussion.
&&
.SYNOPSIS...
The combination of increasing moisture levels and a Pacific
upper-level low pressure system will bring better chances for
showers and thunderstorms on Thursday and Friday over all of
south central Arizona including the Phoenix metro, but southwest
Arizona and southeast California will generally remain dry.
Lingering thunderstorm chances may continue into Saturday before
rain chances decrease for Sunday into the first half of next week.
Temperatures will be below normal for most locations on Thursday
through the weekend before warming back up above normal for the
first half of next week.
&&
.DISCUSSION...
Hi-res models continue to show that thunderstorm chances will be
limited to higher terrain locations north, east, and south of the
Phoenix metro through tonight. The biggest reason for this is
that dynamic forcing that helped generate virga and thunderstorm
activity the past couple of days is generally lacking today as the
region remain in a "col" pattern with little to no dynamic lift.
Essentially, the region is sandwiched between a pair of mid-to-
upper level ridges centered over northern Baja California and the
TX-OK panhandles and a pair of troughs moving into southern
California from the west and Sonora from the southeast. Should
any outflows make it into the Valley this afternoon and evening,
there would be a chance isolated storms could develop. However,
confidence in outflows moving into the Valley currently remains
low. with the latest HRRR making an attempt to move them in from
the NE 1st, then from from the Ajo and Gila Bend areas, that
might be too far southwest of the metro to send a decent outflow
into the Valley this evening.
Much better shower and thunderstorm chances begin as early as
overnight tonight and more likely by Thursday afternoon as the
afomentioned shortwave moves in from the west and the inverted
trough over Sonora moves northwest into southeast Arizona. Ahead
of this inverted trough, an increase in midlevel moisture should
help increase surface-based instability close to 2000 J/kg with
little convective inhibition and PWATs into the 1.6-1.9" range,
along with good mid-level diffluence ahead of a rather deep (for
late-July) upper low approaching the central CA coast. Latest hi-
res model runs have definitely become more bullish on developing a
rather coherent line/cluster of storms moving into the PHX metro
from the southeast and east. The main impacts will be strong
winds, blowing dust, and small hail across the lower deserts and
locally heavy rains across the higher terrain of South-Central AZ.
Although storm motion will be rather rapid for late July (20-30
mph), there is potential for training in areas of favored
orographic lift across southern Gila County. Thus, a Flash Flood
Watch has been issued for the Bush Fire Burn Scar. Also, WPC still
has the region under a marginal risk of excessive rainfall for
Thu/Fri.
Dynamic forcing associated with the inverted trough and the
relatively moist environment should support lingering shower and
isolated thunderstorm activity into the overnight hours on
Thursday into early Friday during which heavy rainfall would be
the primary threat. Friday and Saturday`s forecast is uncertain
given it will depend upon how convection evolves on Thursday
afternoon into the overnight hours, but the setup will still be
favorable for isolated to scattered thunderstorms in the Valley
and greater coverage over the higher terrain provided we remain
unstable without overcast conditions. As synoptic features expand
and contract, there will be fluctuations in how far west the
richer moisture gets with the moisture gradient remaining over
western Arizona. Disturbances within the southwesterly flow aloft
could possibly aid storm development but timing/track/strength of
any of those features that would make a difference is difficult at
the current moment. Regardless, the broader model ensemble is
becoming more confident in a drying and warming trend that will
begin on Sunday and last into the first half of next week as PWAT
values have generally dropped about 0.2-0.3" from what they were
in the previous model cycle for Sunday. Temperatures should
increase back to seasonal normals or slightly above for Monday and
Tuesday with isolated thunderstorm chances confined to the higher
terrain of Gila County.
&&
.AVIATION...Updated at 0020Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
For the remainder of the afternoon and through the evening, aviation
impacts should be on the low side; most convection should remain
well southeast or east of the terminals. Expect FEW-SCT decks
generally aoa 10k feet overnight tonight. Cannot rule out an
isolated shower or storm making it into the Phoenix area, but
confidence too low to mention in the TAFs. Winds will tend to favor
the southwest or west through midnight, but there will likely be
quite a bit of light/variable or variability due to weak outflows
moving in from distant convection. Overall, winds should tend to
transition back to the east after about 08z.
More significant aviation impacts expected by mid afternoon on
Thursday as steering flow becomes stronger and more southerly and a
weather disturbance will be moving in from the south. Expect clouds
to thicken with SCT-BKN decks aoa 10k feet after 14z along with SCT
decks developing around 8k feet. After about 21z, expect isolated
showers or storms to develop and as such have added VCTS to the TAFs
to account for this. At KPHX added a PROB30 for showers, with VCTS
during the evening hours. Potential will develop for stronger
outflow winds into the terminals Thursday late afternoon and
evening, favoring south to southeast, but confidence is a bit too
low and the long time range means those impacts will be left out of
the TAFs with the afternoon package.
Southeast California/Southwest Arizona including KIPL and KBLH:
Conditions look to stay dry over the western deserts with skies
generally clear through Thursday afternoon. Winds will favor the
southeast at KIPL for most of the period, with some southwest wind
possible later this evening into Thursday morning. Speeds should
generally stay 12kt or less. Winds to favor the south at KBLH with
gusty conditions into the evening both today as well as Thursday
afternoon. Peak gusts to exceed 20kt at times.
&&
.FIRE WEATHER...
Saturday through Wednesday:
Monsoonal moisture and isolated to scattered thunderstorms with
below normal temperatures are expected east of the Lower Colorado
River Valley on Saturday, with the best chances over south central
Arizona. Southeast California will remain dry with near normal
temperatures during this time while temperatures over the lower
deserts of Arizona remain below normal. Minimum relative humidity
values will generally be in the 20-30% range across the lower
deserts through Saturday with values in the teens over southeast
California and above 30% over the higher terrain of Gila County.
Overnight recovery above 30% is expected for all locations with
values above 50% over the higher terrain of Gila County. A drying
and warming trend will begin on Sunday through the Wednesday
across the entire region, with only isolated thunderstorms
expected over Gila County. Diurnal winds are generally expected
aside from any gusty outflows associated with thunderstorms.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flash Flood Watch (Bush Fire Bush Scar) from Thursday
afternoon through Thursday evening for AZZ547-556-557.
CA...None.
&&
$$
DISCUSSION...Percha/Hopper
AVIATION...CB
FIRE WEATHER...Hopper
Area Forecast Discussion
National Weather Service Shreveport LA
1005 PM CDT Wed Jul 22 2020
.SHORT TERM.../Tonight/
The convection has diminished this evening, a bit sooner than what
was observed 24 hrs ago, with the bndry lyr having quickly cooled
near the remnants of a weak shear axis over portions of Srn AR
and N LA. The earlier runs of the global models as well as the
latest 00Z NAM continue to suggest that isolated convection may
redevelop overnight near this weak shear axis over SE OK/portions
of extreme NE TX/SW AR/extreme Nrn LA, with even the latest run of
the HRRR suggesting this as well, and thus have retained slight
and low chance pops tonight across these areas to account for this
possibility. Unfortunately, the rain may be harder to come by
Thursday as this shear axis dissolves in response to the
amplifying upper ridge over the Srn Plains which will expand E to
the Mid-South region, thus suppressing most convection development
while in turn, resulting in an increase in the heat. Did not make
much adjustments to the forecast min temps tonight, with temps
expected to range from the lower to mid 70s once again. While the
heat will return Thursday, convection should increase across
portions of E TX/N LA/Srn AR Friday N of newly formed TD 8 in the
Cntrl Gulf, which will continue W towards the TX coast through the
weekend.
Zone update already out...grids will be available shortly.
15
&&
.PREV DISCUSSION... /issued 644 PM CDT Wed Jul 22 2020/
AVIATION...
VFR conditions should continue through much, if not all of the
23/00Z TAF period. The convection continues to quickly diminish
across the region early this evening, although convective debris
will linger through the overnight hours. Some isolated SHRA
redevelopment will be possible though overnight across portions of
extreme NE TX/SW AR/NW LA near a weak disturbance aloft, but low
confidence precludes mention in the SHV/TXK terminals attm. Some
patchy FG/BR will be possible late tonight in areas that received
rain earlier today, with brief IFR/low MVFR cigs possible
around/shortly after daybreak Thursday before scattering out by
mid-morning. A sct cu field is expected by late morning through
the afternoon, with isolated convection possible across portions
of extreme NE TX/SE OK/SW AR near the weakening upper level
disturbance, as well as across the Srn sections of Ncntrl LA well
N of a slowly developing low pressure system drifting W across
the Cntrl Gulf. Any convection though should diminish by early
evening. Lt/Vrb winds tonight will become SE 4-8kts after 15Z.
/15/
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 75 93 76 91 / 10 20 0 50
MLU 75 95 75 92 / 20 30 10 60
DEQ 73 90 73 92 / 30 30 0 20
TXK 73 91 75 90 / 20 20 0 20
ELD 72 94 73 92 / 20 20 10 30
TYR 75 93 75 90 / 10 10 0 30
GGG 74 93 75 91 / 10 10 0 40
LFK 74 93 76 90 / 10 10 10 70
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&
$$
15