Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/14/18
Area Forecast Discussion
National Weather Service Columbia SC
740 PM EDT Fri Apr 13 2018
High pressure centered off the coast will continue ridging into
the southeastern states through Saturday. This will produce
southerly flow over the region along with a warming trend. A
cold front will cross the area Sunday into Sunday night bringing
showers and thunderstorms. Dry weather and cooler temperatures
will arrive Monday with moderating temperatures through the
middle of next week.
.NEAR TERM /UNTIL 7 AM SATURDAY MORNING/...
Surface high pressure situated off the Southeastern Coast will
continue to promote southerly flow into the forecast area
overnight. Clouds are expected to increase towards daybreak.
Increasing clouds and mixing should promote mild overnight low
temperatures, in the upper 50s to around 60.
.SHORT TERM /7 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
Winds out of the south on Saturday will bring additional
moisture into the region through the day. PWAT readings climb to
around an inch, but with model soundings still showing a good
capping inversion in mid-levels, do not expect any precip
through the day. Temperatures will be rather warm during the
afternoon on Saturday, with readings into the middle 80s common.
Saturday night should also remain mostly dry for majority of the
night. For that time, models do show some rainfall around the
region, but keep much of it closer to the mountains, and also
along the coast. Exception will be closer to sunrise Sunday
morning when isolated showers may be able to move into the
forecast area. Overnight lows mainly in the middle 60s.
Sunday is the day of interest. A cold front will be approaching
the region from the west, while a strong upper trough will push
eastward also. The upper trough appears to have a negative tilt
to it west of the area by the afternoon as the front
approaches. Low-level winds become rather strong, and moisture
continues to increase in advance of the front. Best chance for
stronger activity should be during the late afternoon and
evening hours as a potential squall line moves through. SPC has
the area outlooked in a Day 3 slight risk. Damaging winds will
be the main threat. Will continue high pops across the cwa on
Sunday, but have tried to narrow down some of the timing and
movement a little bit better. Lower pops in the morning, with
increasing pops during the afternoon associated with the line,
then a decrease in pops Sunday night as the front moves east.
.LONG TERM /MONDAY THROUGH FRIDAY/...
Behind the exiting cold front, generally fair conditions
expected to persist through the longer term period.
High pressure will build into the region behind the front on
Monday, with the potential for windy conditions during a good
portion of the day due to a tight pressure gradient over the
region. Winds weaken Monday night, then become lighter for the
remainder of the period. The airmass appears to remain dry at
this time through the end of the week, so no rainfall expected,
even with a weak cold front during the middle of the week.
Temperatures will be cooler on Monday behind the front, then a
warming trend begins on Tuesday, lasting through the end of the
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions through most of the TAF period although some
stratus possible early Saturday morning mainly near OGB.
Pressure ridge continues offshore of the Carolinas. Cumulus
clouds diminishing with loss of heating so expect mainly clear
sky during the evening. Winds will diminish to south- southeast
less than 10 knots. Models suggest a relatively strong low level
jet...20 to 30 knots overnight which should limit fog despite
modest increase in low level moisture due to onshore flow. There
is some guidance mainly HRRR suggesting some stratus with
IFR/MVFR possible ceilings around daybreak mainly near OGB
terminal. MVFR visibility restriction also suggested at AGS/OGB
although low level jet should be a limiting factor. So brief
period of MVFR forecast in those areas around 12z...otherwise
VFR with scattered to broken cumulus developing by late morning.
South winds will increase to 10 to 15 knots Saturday afternoon.
EXTENDED AVIATION OUTLOOK...Restrictions expected Sunday and
Sunday night as a cold front crosses the region along with
showers and thunderstorms. Strong and gusty winds expected
Sunday through Monday.
Area Forecast Discussion
National Weather Service Des Moines IA
711 PM CDT Fri Apr 13 2018
Issued at 426 PM CDT Fri Apr 13 2018
Bottom Line up Front...
Severe Weather main threat in southern Iowa for the immediate
short- term. Large hail, tornadoes, and damaging winds all
possible. Transition to winter weather hazards overnight across
northern to northwestern Iowa.
20z Sfc analysis has roughly a 990mb low positioned over
southeastern Nebraska/northeastern Kansas. Well-advertised
moisture has surged ahead of this low into the warm sector, aided
by 50 to 60 kt moisture transport winds. All eyes have been on how
far north the warm front (oriented from west to east) attendant
to the sfc low would make it today. At present time, the boundary
is draped around the southern three tiers of counties in Iowa.
South of the boundary, dewpoint temperatures have climbed into the
60s. Much of southwestern Iowa had sunshine through this morning
which aided in destabilization. Convective initiations is well
underway from southwestern Iowa southward through Kansas.
Ongoing Severe Weather...
With ongoing convection, focus is on mode and longevity. Latest
RAP showing widespread CAPE values of 2000 J/Kg. 0-6KM shear is
upwards of 50 kts and low-level helicity is off the charts. With
this moisture, sounding profile, LCL heights are more than
sufficiently low for tornadoes... especially near to the
boundary. Hodograph analysis has slowed down storm motion to more
the 30 to 40 mph range vs the 50 to 60 mph range they were
suggesting yesterday. Storms getting north of the boundary will
lose their tornado potential, with elevated hail being the main
Into the overnight, boundary layer won`t decouple, so we won`t have
capping issues. Instability lingers, though waning through 12z Sat.
The boundary is slated to slowly drift southward, making it into
Missouri between 06z Sat and 09z Sat, which will bring an end to the
SVR/Tor threat. Will have to keep an eye on storms in
Kansas/Missouri moving northward... with such prolific shear
profiles, storms should be able to sustain themselves into Iowa.
.LONG TERM.../Saturday through Friday/
Issued at 426 PM CDT Fri Apr 13 2018
Bottom Line up Front...
Winter weather hazards continue tonight through Sunday, with
blizzard potential likely in northwestern Iowa. Strong winds will
be major driver of impacts.
Transition to snow should begin in northwestern Iowa around 12z Sat
as CAA begins to infiltrate Iowa. Minor tweaks made to the forecast
from the previous days... the biggest of which has been to beef up
amounts slightly in northwestern Iowa. In short, there has been a
trend to linger instability through Iowa as major ascent processes
in play. Thundersnow remains very possible, which typically
indicates upwards of 2 inch per hour rates. High confidence in winds
remaining in the 25 to 35 mph range, with gusts upwards of 50 mph in
northwestern Iowa. Winds will be the biggest driver of impacts, as
visibility will approach zero during heavier periods of
snow...likely in the Saturday Morning to Saturday afternoon
timeframe. This would have significant impacts on travel, making
travel very dangerous and nearly impossible in certain locations. As
our sfc low pulls away to the east, snowfall intensity/rates will
begin to diminish Saturday afternoon into the evening hours.
Another forecast tweak has been to linger the snow into Sunday. The
12z NAM especially keeps some forcing in our eastern counties
through at least 18z Sun. Winds should be around 15 to 25 mph during
this timeframe, so there may still be travel impacts as visibility
could drop to less than one mile at times.
Monday and Beyond...
High pressure moves in to melt snow and quiet the weather on Monday.
Long-term models have consistently been showing the next systems to
push through the upper Midwest on Wednesday and on Saturday. At this
time, it appears these should be fairly low-impact systems, with
rain and a possible light rain/snow mix during the overnight hours
Tuesday night and Friday night.
.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 711 PM CDT Fri Apr 13 2018
IFR conditions and strong, gusty winds are in place across
northern Iowa, somewhat removed from a west to east warm front
currently between KCNC and KOXV. Confidence is high that these
conditions will persist and sag southward somewhat later this
evening. Thunderstorms producing producing severe wind gusts at
times with variable conditions will also continue from western
into northern Iowa. Later tonight strong winds will persist north
with strong winds continuing north leading to blizzard conditions
north and west with IFR or less likely.
Issued at 458 PM CDT Fri Apr 13 2018
Wet period expected over the next couple days with seasonally
moderate to heavy QPF expected across the northern CWA. In response,
the 2-day QPF hydrograph ensembles show significant within-bank
rises at many forecast points within the Cedar, Iowa and Des Moines
River basins mainly along and north of US Hwy 20, with the exception
being the Des Moines River at Des Moines SE 6th St where the river
may come within a couple feet of flood stage.
The 2-day QPF hydrograph ensembles suggest flooding is possible at a
few locations in the Cedar and Des Moines River basins along and
north of US Hwy 20. A Flood Warning has already been issued for the
West Fork Des Moines River at Estherville. In addition, a Flood
Watch has been issued for the Cedar River at Cedar Falls.
Winter Weather Advisory from 7 AM Saturday to 1 AM CDT Sunday
Blizzard Warning from 7 AM Saturday to 1 AM CDT Sunday for
Winter Weather Advisory from 7 AM Saturday to 1 PM CDT Sunday
Winter Storm Warning from 7 AM Saturday to 1 AM CDT Sunday for
Winter Weather Advisory from 1 AM to 1 PM CDT Sunday for IAZ007-
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1019 PM CDT Fri Apr 13 2018
See Fire Weather section below for the primary update purpose. One
quick note on the ZFP update is that evening post-frontal winds are
stronger, and the area of storm chances late tonight was expanded a
few counties westward.
The cold front overtook the dry-line and generate quite a windy
condition over the southern Edwards Plateau, and perhaps brought
slightly stronger storms and convection inititation to expand
westward. The RFW for the evening was thus extended east to include
Llano, Uvalde, and Eagle Pass. Brief near critical fire weather
conditions could extend east into the I-35 corridor overnight, but
will be more likely after sunrise Saturday. To avoid confusion, the
Fire Weather Watch will not be upgraded until after the 2am RFW is
set to expire.
.PREV DISCUSSION... /ISSUED 655 PM CDT Fri Apr 13 2018/
AVIATION... /00Z TAFS/
Brief towering cumulus formed near DRT but has since waned with no
new cell development expected. Along I-35, cell development over the
Hill Country and rapid refresh model tracking of the propagation would
suggest some impacts to reach AUS, with the model showing weaker
convection forming with the fropa around SAT/SSF. Improving sky
condition should occur quickly in the wake of the front, but a brief
period of mvfr cigs near the front will be possible. Gusty winds are
forecast after daybreak possibly over 25 knots at AUS.
PREV DISCUSSION... /ISSUED 255 PM CDT Fri Apr 13 2018/
SHORT TERM (Tonight through Saturday Night)...
The associated mid level shortwave, which generated the elevated
convection earlier along the I-35 corridor, is continuing northeast
out of the CWA. A weakening of the cap took place across the northern
CWA as it passed, confirmed by aircraft soundings out of AUS, and
clearing should help to continue a gradual weakening as the dry line
approaches from the west. The dry line is currently nearing a
Rocksprings to Del Rio line mid afternoon and will continue east
through the remainder of the afternoon. CU is becoming slightly
agitated across the northeast Hill Country, but so far aforementioned
cap is preventing deeper convection from developing. As cap weakens
through the remainder of the afternoon there is a slight chance of
getting deeper convection and a storm or two ahead of the dry line
across the northern CWA. A conditional severe threat for large hail
exists given CAPE values of 3000-4000 J/kg and deep layer shear
values in excess of 40 kts.
12Z runs of HREF members as well as recent HRRR runs develop
convection later this evening near and east of I-35 as forcing from
the front, catching up to the dryline, and tail end of shortwave are
able overcome what is left of the weakening inversion. However, each
model initiates the isolated convection in different areas along the
I-35 corridor, before increasing in coverage ahead of the front east
of I-35 overnight. Again, a strong to severe threat is in play with
any storms that develop, with hail and straight-line winds the
Farther west, winds should be increasing through the remainder of the
afternoon across the far western third of the CWA, and a critical
fire danger should develop thorugh the later afternoon and into the
evening in counties currently in the Red Flag Warning.
Cooler, dry, and breezy to windy conditions will develop behind the
front on Saturday. Elevated to near critical fire weather conditions
are possible across portions of the area and will address further in
the Fire Weather section below.
LONG TERM (Sunday through Friday)...
A cold morning on Sunday, and model guidance has trended colder on
morning lows for the Hill Country now showing mid 30s in many areas.
Winds speeds will play a large role in how far temps bottom out. NAM
MOS, which indicates winds dropping of to nearly calm across the
northern Hill Country, is indicating the potential for near freezing
temperatures across Kerr and Gillespie counties. Elsewhere winds
should stay up enough, but still cool in the low to mid 40s outside
of the Hill Country Sunday morning. The dry air in place and clear
skies should lead to a large diurnal swing in temperatures, with
highs Sunday afternoon back into the 70s, and even some lower 80s
along the Rio Grande.
Dry and warmer conditions for Monday and Tuesday, and a breezy
southerly wind could lead to elevated fire weather conditions in some
Increasing low level moisture will take place Tuesday night into
Wednesday with a weak cold front slipping through or stalling over
the area Wednesday and Wednesday night. A stronger upper level system
will develop to the west Friday into Saturday with better chances
for precipitation over the area as it approaches.
A dry-line is currently moving through Val Verde and Edwards counties
and will continue east through the remainder of the afternoon and
evening. Gusty west and northwest winds and very low relative
humidity values will continue to develop behind it this afternoon and
evening. Wind gusts around 30 mph and RH values bottoming out around
5 to 15 percent will develop through the late afternoon. When
combined with dry fuels this result in critical fire weather
conditions and a Red Flag Warning remains in effect for Val Verde,
Kinney, and Edwards counties.
A cold front is forecast to move through late tonight. Strong north
winds will develop behind the front on Saturday, with drier air
filtering into the rest of the region. Wind gusts to around 30 mph
with minimum RH values in the teens to 20s will result in elevated to
near critical fire weather conditions on Saturday. A Fire Weather
Watch is in effect for areas near and west of I-35 and could be
upgraded to a Red Flag Warning tomorrow.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 77 71 45 73 47 / 30 - 0 0 0
Austin Bergstrom Intl Airport 75 70 40 72 43 / 40 - 0 0 0
New Braunfels Muni Airport 75 72 41 75 45 / 40 0 0 0 0
Burnet Muni Airport 81 68 40 71 44 / 20 0 0 0 0
Del Rio Intl Airport 85 77 47 81 52 / 0 0 0 0 0
Georgetown Muni Airport 77 68 40 71 43 / 30 - 0 0 0
Hondo Muni Airport 81 76 41 80 47 / 20 0 0 0 0
San Marcos Muni Airport 76 71 41 74 44 / 40 - 0 0 0
La Grange - Fayette Regional 77 69 42 70 44 / 50 10 0 0 0
San Antonio Intl Airport 77 74 44 76 49 / 30 0 0 0 0
Stinson Muni Airport 81 75 45 77 49 / 30 - 0 0 0
Fire Weather Watch from Saturday morning through Saturday evening
Red Flag Warning until 2 AM CDT Saturday for Bandera-Edwards-
Public Service/Data Collection...Williams
Area Forecast Discussion
National Weather Service Lincoln IL
844 PM CDT Fri Apr 13 2018
Issued at 831 PM CDT Fri Apr 13 2018
Scattered showers and storms continue to track north to northeast
across west central Illinois with a larger area of showers and
storms over central and southern Missouri heading northeast
towards our area. A frontal boundary edging slowly south into
our area again this evening with the winds at Galesburg and
Lacon into the east with temperatures 50 to 75 miles north
of the boundary in the middle 40s. As the wave of showers
and storms to our southwest tracks over our area later this
evening and overnight the boundary will hold nearly steady
but then, as the showers shift off to our east Saturday morning,
the front will begin to drift south.
Just where the boundary ends up in central Illinois will make a
big difference not only in temperatures Saturday, but where the
threat for severe storms sets up Saturday afternoon. Tonight`s
storms could still produce some isolated gusty winds and hail but
tomorrow afternoon`s threat will include an isolated tornado along
the frontal boundary as weak low pressure moves along the stalled
front over central Illinois.
Have made some adjustments to the temperatures across the north
for the rest of the evening along with increasing the POPs across
the west and north where we were already seeing shower activity.
We should have the update out by 9 pm.
.SHORT TERM...(This evening through Saturday)
ISSUED AT 241 PM CDT Fri Apr 13 2018
Warm front has drifted about 10 miles north of the far northern
CWA border early this afternoon, roughly aligned just south of
I-80. Showers and scattered thunderstorms have continued to push
northeast, and were largely contained to areas north of I-72 at
2:30 pm. A lull in the rain is anticipated into early evening, as
the convection ahead of the front in Missouri starts to get
organized. NAM and the ARW/NMM have this arriving shortly after
sunset, while the HRRR favors more of a late evening approach. As
the surface low move into northern Missouri overnight, the bulk of
the rain will be confined to the east half of the forecast area.
The front should drift back southward late in the night, remaining
quasi-stationary from about Quincy-Bloomington most of the day.
Have cut back on thunder chances Saturday north of this boundary,
but kept showers and storms further south. Latest SPC Day2 outlook
keeps the slight risk of severe storms over the eastern CWA. GFS
progs show surface CAPE of around 1500 J/kg in that area by early
afternoon, though the NAM has dialed things back considerably.
With the front over the northern CWA, a fairly sizable temperature
gradient will be in place. Far northern CWA should stay fairly
steady in the mid 40s on Saturday, while the south gets close to
.LONG TERM...(Saturday night through Friday)
ISSUED AT 241 PM CDT Fri Apr 13 2018
Large upper low with this storm system will be in no particular
hurry to exit the area, with the synoptic models centering it
somewhere near the southern Michigan border by early Monday.
Scattered showers will continue through the weekend as this
feature passes, most numerous from about Peoria northward. Cold
air being drawn in behind the low still looks to be sufficient to
cause a changeover to snow Sunday night, though amounts should be
negligible. Temperatures should be down into the 20s by Monday
morning, threatening any gardens that have been planted in the
recent mild spell.
Mid week storm system has trended a bit further south, though the
models do have decent agreement in much of the precipitation
staying north of the low track. Have included a chance of showers
north of I-74 Tuesday night, but conditions should be largely dry
next week, once the upper low exits. A cooler period is expected
in the wake of the mid week system, not especially cold but enough
that some frost may be a concern.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 602 PM CDT Fri Apr 13 2018
Main forecast challenge this period will be timing of showers and
thunderstorms into the forecast area later this evening and how
quickly cigs drop to MVFR and IFR, especially across the north in
PIA and BMI. A frontal boundary is expected to slowly edge south
tonight with IFR cigs to the north of the boundary while MVFR and
low VFR cigs dominate to the south. Question is how far south this
boundary will go later tonight into Saturday morning as low
pressure approaches from the west. Most of the operational models
suggest it will move to south of a BMI to PIA line and approach
CMI and AAA by Saturday morning. The surface low will track right
along the boundary tomorrow with our northern TAF sites possibly
staying in MVFR to IFR while further south, we may see cigs pop
up to low VFR for a time. Shower timing looks to be in the 02z to
05z time frame from southwest to northeast with a lull in the
precip around 12z Saturday with chances low enough during the
day to continue with VCSH at this time.
The gusty southerly winds will gradually back into a east to
southeast direction later this evening in PIA and BMI and after
09z in our southern TAF sites. Depending on where the front
actually ends up tomorrow, winds will vary from east to northeast
at PIA and BMI and southeasterly at SPI, DEC and CMI. Wind speeds
tonight will range from 12 to 17 kts with gusts up to 25 kts at
times, especially in SPI, DEC and CMI. Wind gusts should start to
settle down after 03z across the north and by 08z in our southern
Area Forecast Discussion
National Weather Service Jackson MS
1024 PM CDT Fri Apr 13 2018
...SEVERE STORMS AND FLASH FLOODING TONIGHT THROUGH SATURDAY...
Updated for evening discussion.
Showers and thunderstorms will continue moving into the region
tonight in association with a strong cold front. All modes of severe
weather will be possible, along with flash flooding. The current
forecast is in good shape with no changes needed. /27/
Prior discussion below:
Tonight through Saturday night...
Satellite imagery and RAP analysis shows a digging trough exiting
out of the Desert Southwest and into the Southern Plains with large
scale ascent overspreading a large portion of the Great
Plains/Midwest. This trough and associated closed mid/upper-level
low and strong cold front will be the driver for the expected severe
weather tonight through Saturday. Dry weather will persist across
the vast majority of the ArkLaMiss the rest of this afternoon into
the early evening hours. As previously mentioned yesterday, guidance
has continued to hone in on the slower timing with ongoing
convection over the ArkLaTex progged to enter the Delta between 10pm
Severe threat tonight: deep layer shear of 40-50kts, strong 0-1km
shear and helicity, and ample SBCAPE up to 1500 J/kg will support
all modes of severe weather as convection enters the Delta. 12z hi-
res CAM guidance has come into better agreement with respect to
convective evolution with a slow moving broken line of storms being
the primary storm mode. Potential will also exist for
discrete/scattered supercells ahead of the line with embedded
supercell structures in the line itself. Given the aforementioned
environment, all modes of severe weather including tornadoes, some
of which could be strong, hail up to golf ball size, and damaging
winds up to 70mph are expected. The greatest potential for a strong
tornado will be with any discrete supercells ahead of the line.
There is also indication that the northern portion of the line could
accelerate along and north of the Hwy 82 corridor with an associated
damaging wind threat extending slightly further east. This
convection will be aided by a surge of 850mb ThetaE, however the
ThetaE minimum in its wake will also help to limit eastward
progression overnight. Given the slow progression, expect
convection to be located in the vicinity of a line from Grenada to
Natchez by sunrise Saturday morning. After collaboration with
SPC, the ongoing enhanced risk appears well placed and the only
changes will be to update the timing to reflect the slower
Severe threat Saturday: the slower timing will allow for severe
storms to persist through the day Saturday with convection located
in the vicinity of the aforementioned line by sunrise. A ThetaE
minimum will be located ahead of the ongoing line of storms during
the early morning hours, however another surge of higher ThetaE air
(upwards of 340 K) and renewed ascent will quickly overspread south
and east portions of Mississippi by the mid morning hours. This will
help to reinvigorate convection with the severe threat quickly
increasing. Multiple hi-res CAM families indicate the potential for
discrete/scattered supercell development ahead of the line during
the mid to late morning hours roughly along and southeast of the
Natchez Trace corridor. The environment will remain very favorable
for severe weather with a stout 50 to near 60kt low-level jet in
place which will help to enhance/enlarge hodographs. Once again, all
modes of severe weather including tornadoes, some of which could be
strong, hail up to golf ball size and damaging winds up to 70mph are
expected. These storms are progged to congeal into a broken line by
the early afternoon hours before finally exiting the area into
Alabama by late afternoon/early evening. The ongoing enhanced area
is also well placed to cover the threat with the only changes to
update the timing.
Flash flooding threat: anomalous deep moisture and multiple surges
of 850mb ThetaE will combine with slow moving/training storms
with high precipitation rates and will result in widespread 3-5"
of rainfall with locally higher amounts. This will lead to flash
flooding concerns across the ArkLaMiss tonight through Saturday.
There are two main areas of focus for the heaviest rainfall, the
first is tonight over northwest portions of the Delta generally
along and northwest of a line from Richland Parish to Sunflower
County. Strong consideration was given to upgrading this area to a
significant threat in the HWO/graphics, however guidance has
struggled spatially with the exact placement of highest totals so
held off on any upgrades for now. The second area of concern will
be Saturday along and east of a line from Brookhaven to Columbus.
After collaborating with WPC and neighboring offices, a portion of
this area will be added to a moderate risk for excessive
rainfall. A significant threat for flash flooding was also
considered for this area but once again, spatial uncertainties
with exact placement of the higher amounts precluded an upgrade
with this forecast issuance. However, if confidence in placement
of a swath of higher totals becomes apparent an upgrade to the
HWO/graphics could be needed later tonight.
Storms and rain should slowly exit the area into Alabama by late
afternoon to early evening on Saturday. Cooler and drier air will
advect in behind the cold frontal passage with low temperatures
dropping off into the low to mid 40s across much of the area by
Sunday morning. /TW/
Sunday through next Thursday:
Overall in the wake of the significant cold front & severe weather,
expect much cooler and drier conditions. As the cold front &
longwave trough digs through the region on Sunday morning, expect
continued cold air advection and some cloud lingering over the east-
northeastern areas on Sunday. Due to colder thermal profiles, highs
will only reach the mid 50s-low 60s. This is some 15-20 degrees
below normal and could reach the top 5 coolest high temperatures for
As strong surface high builds into the region and troughing builds
to the east, expect lows to fall well below normal into the mid-
upper 30s (~15 degrees below normal) and possibly into the top 5
coolest low temperatures. In addition, if the gradient can be a
little lighter, we may be able to get some patchy frost. This would
mainly be confined along and north of I-20 and east of I-55. For
now, due to some gradient & winds around, will only mention in the
weather grids but hold off on anything in the HWO/graphics. But will
monitor trends as we go forward. As the surface high and mid-level
ridging build into the area by early-mid week (Tuesday-Thursday),
expect efficient mixing and warmer temperatures. We could warm well
into the mid-upper 70s to near low 80s by midweek. In addition, a
weak cold front will move through the region on Wednesday but with
limited moisture (PWs only around an inch to an inch and a quarter_
only a few showers & increasing clouds may be possible. Capped off
PoPs at slight chance as it moves through on Wednesday. As the
trough digs to our northeast & weak frontal boundary moves through
on Wednesday, expect surface ridging to build in the wake and clouds
to clear out. Due to slightly cooler thermal profiles, expect
temperatures to be slightly cooler but still near normals. /DC/
00Z TAF discussion:
Ceilings will steadily lower this evening in advance of a cold
front moving in from the west. As thunderstorms increase, MVFR/IFR
conditions will develop and linger for a few hours as storms
slowly move through. Post storm showers will keep conditions at
MVFR, but improving conditions will be seen thereafter as the
front moves through. Southerly winds ahead of the boundary will
generally range from 10 to 20 knots with gusts 30 to 35 knots./26/
.PRELIMINARY POINT TEMPS/POPS...
Jackson 70 72 43 58 / 28 100 44 5
Meridian 69 75 46 61 / 30 97 85 9
Vicksburg 68 70 42 59 / 67 83 22 4
Hattiesburg 71 76 48 63 / 23 99 83 6
Natchez 67 71 41 60 / 60 89 28 2
Greenville 66 69 42 55 / 92 72 19 3
Greenwood 68 70 42 55 / 83 94 34 5
MS...Flash Flood Watch through Saturday evening for MSZ018-019-
LA...Flash Flood Watch through Saturday evening for LAZ007>009-015-
AR...Flash Flood Watch through Saturday evening for ARZ074-075.
Area Forecast Discussion
National Weather Service Lake Charles LA
1015 PM CDT Fri Apr 13 2018
Wx map shows sfc low over N MO, with cold front extending
southward across eastern KS/OK and C to N TX. Radar only showing
showers across inland SE TX and C LA this evening. The stronger
storms remain across NE TX/N LA. Latest HRRR guidance on track to
push the front and developing line of strong to severe TSRA
approaching our warning area of Inland SE TX by 1-2 AM, pushing
through the remainder of SE TX/C and S LA. Severe threat with this
convection still present. SPC has issued TORNADO WATCH 45 until 6
AM CDT Saturday for Hardin, Jasper, Newton and Tyler counties in
SE TX, and Rapides, Beauregard, Vernon parishes in Western and
Short term updates to forecast, mainly for temp/dewpoint refresh,
but otherwise on track. Rainfall amounts, and timing of greatest
chances of showers and thunderstorms remain on track.
.PREV DISCUSSION... /issued 608 PM CDT Fri Apr 13 2018/
AVIATION...MVFR ceilings are expected through midnight with IFR
ceilings possible during the early morning. Ceilings will improve
a few hours after FROPA Saturday Morning. Showers and storms have
begun across the area, but mainly in SETX and CenLA. Chances will
increase across the remainder of the area through the evening.
Coverage will decrease from west to east through the morning.
South winds will quickly veer NW with the front.
PREV DISCUSSION... /issued 411 PM CDT Fri Apr 13 2018/
-Scattered to numerous severe storms will be possible overnight
through Saturday as a cold front moves across the region
-Damaging winds will be the primary threat with overnight
thunderstorms, but tornadoes and large hail will also be
-There will be a 10-20% chance of flash flooding overnight and
Saturday, with the greatest chance across far eastern Acadiana
-Storm total of rainfall of 1-3 can be expected with isolated
higher totals of 5+.
Short TermTonight and Saturday...
Radar and satellite imagery over the past several hours show
convection has developed across portions of the Lower Mississippi
River Valley and Central Plains. These strong to severe
thunderstorms are expected to continue to develop through this
evening as a the combination of a dryline and cold front pushes
eastward into the Arklatex region. Deep layer shear in excess of
40 knots aligned parallel to the front/dryline should result in
upscale growth of initial convection into an organized line. The
latest round of 12Z HREF guidance depicts such an evolution with a
line of thunderstorms moving through the CWA overnight tonight
and exiting Acadiana Saturday afternoon. As far as timing of this
event, the greatest potential for strong to severe thunderstorms
across portions of the area will be as follows:
Interior Southeast Texas/Piney Woods: 11 PM 4 AM
Alexandria Lake Charles Beaumont: 3 AM 7 AM
Acadiana: 6 AM Afternoon
SPC has most of the area highlighted in a Slight Risk of severe
of severe thunderstorms tonight and through tomorrow. The far
southeastern portion of the CWA is highlighted in an Enhanced Risk
based on the potential for restrengthening of thunderstorms
tomorrow afternoon. The primary threat with thunderstorms tonight
will be damaging winds. In addition to damaging winds, 0-1 km and
0-3 km storm relative helicity in excess of 200 m2/s2 will
supportive of tornadoes with any bowing portions of the QLCS/LEWP
that develop. While large hail cannot be ruled out, based on the
predominant linear convective mode, it should be the least likely
of the severe weather threats. The best chance for large hail will
be with any isolated cells that can develop ahead of the main
line late tonight across SE Texas/Central Louisiana or across far
eastern Acadiana/Southeast Louisiana on Saturday.
This morning`s 12Z LCH and model forecast soundings all indicate
that a deep warm cloud layer will be in place over the region which
will be supportive of efficient precipitation production. While
the squall line should be fairly progressive, a widespread 1"-3"
of rainfall is expected with local amounts in excess of 5 inches
possible. Currently, 3-hour flash flood guidance across the
region ranges from 3.5-5 inches. The 12Z HREF guidance had a
10%-30% chance of rainfall exceeding these values across portions
of southeastern Acadiana tomorrow and this corresponds well with
the Slight Risk of Excessive rainfall issued by WPC. At this
point, while flash flooding will be possible tomorrow, the threat
does not appear to be widespread enough to warrant a Flash Flood
Watch at this time.
Rainfall is expected to gradually come to an end from west to east
Saturday afternoon as the cold front exits the region. Behind the
front much cooler, drier air will filter in on brisk northerly
winds Saturday into Sunday.
Long TermSunday through Friday...
An upper level ridge will build across the central CONUS in the
wake of the trough that will bring tonight`s cold front. Surface
high pressure will result in dry conditions and cooler
temperatures on Sunday and Monday. Temperatures will begin to
moderate through the middle part of the week but conditions should
remain predominately dry with relatively zonal 500 hPa flow in
place over the central US. The next substantial shortwave trough
is expected to approach the region next weekend brining another
chance for showers and thunderstorms.
Strong onshore flow will persist through the evening in advance
of an approaching cold front. A broad line of thunderstorms is
expected tonight into Saturday with the frontal passage. Strong
offshore flow will develop in the wake of the front late Saturday.
Northerly winds of 20-25 knots with gusts to 35 knots and seas of
4-8 feet with seas up to 10 feet will be possible. Strong offshore
flow will persist into Sunday before relaxing on Monday afternoon
as high pressure once again settles over the region. Therefore,
the Small Craft Advisory currently in effect through Saturday
night will likely be extended.
.PRELIMINARY POINT TEMPS/POPS...
AEX 64 70 42 63 / 90 60 10 0
LCH 65 71 45 66 / 90 60 10 0
LFT 68 72 44 63 / 50 90 20 0
BPT 62 70 43 66 / 90 40 0 0
GM...Small Craft Advisory until 1 AM CDT Sunday for GMZ450-452-455-
Small Craft Exercise Caution through late Saturday night for
Area Forecast Discussion
National Weather Service Saint Louis MO
412 PM CDT Fri Apr 13 2018
.SHORT TERM... (Through Late Saturday Afternoon)
Issued at 411 PM CDT Fri Apr 13 2018
Deep closed low aloft over the northwest Kansas is winding its way
slowly to the east. The surface low is now over southeast Nebraska
with the trailing cold front/dryline moving into eastern Kansas.
Several clusters of thunderstorms have formed along and ahead of the
front in Kansas, Oklahoma and Arkansas. After some divergence
earlier in the day, the CAMs are mostly centered around the idea
that the thunderstorm clusters will solidify into line that will
move through lower and mid Mississippi Valley this evening. RAP CAPE
forecasts this evening really fall off after 02-03Z...so not sure
how much potential for severe weather there is...and fairly
substantial surface based CINH remains in place into the evening.
Therefore, think the storms will be weakening as they move into our
CWFA after 00-01Z. That being said, ~1000 J/Kg MUCAPE and 45+kts of
deep layer shear is plenty for a few severe storms. Will have to
initially watch for both damaging wind and large hail, but the wind
threat should diminish as the evening progresses and the boundary
layer stabilizes. The stratiform precip region behind the line of
convection may linger over our eastern Illinois counties and
southeast Missouri til near daybreak on Saturday morning, but much
of the CWFA should be dry.
The cold front will continue moving east on Saturday morning and
should be through central Missouri by 15-16Z. Another round of
thunderstorms is possible along and ahead of the cold front
Saturday...and there is another severe threat over parts of central
Illinois near the tipple-point just ahead of the low where mid
level lapserates approach 9C. Think the primary threat will be large
hail due to the steep lapserates, but 0-6km shear is approaching
50kts and the the cold/warm front interface will be near there as
well which will add additional low level vorticity. Will have to
watch closely for possible supercell development.
.LONG TERM... (Saturday Night through Next Friday)
Issued at 411 PM CDT Fri Apr 13 2018
An upper trough and low pressure system will move across north central
Missouri and western Illinois on Saturday night into Sunday. Some wrap
around moisture and strong cold air advection will provide for a chance
of a brief rain/snow mix over the northern two thirds of the forecast
area on late Saturday night into Sunday morning. The precipitation type
will then be all liquid shortly after sunrise on Sunday. All
precipitation will exit the forecast area by Sunday night. High
pressure will move into the Central Plains immediately behind the
exiting upper trough by late Sunday night into Monday morning.
The weather will remain dry on Monday as high pressure moves away
from the forecast area. A cold front and attendant low will
approach the forecast area on Tuesday night into Wednesday. At
this time, it appears only scattered showers will be possible in
far north central Missouri on Tuesday night into Wednesday. The
cold front is expected to clear the area by Wednesday afternoon.
High pressure will move south from the Northern Plains into the
Central Plains, then to the Ohio Valley by Friday afternoon.
Temperatures will climb from below climatological average at the
end of the weekend to at or above normal values through the middle
of next week.
.AVIATION... (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1249 PM CDT Fri Apr 13 2018
Showers and a few thunderstorms will continue to move north-
northeast across northeast Missouri and west central/south central
Illinois this afternoon. The rain is very light at this time, so
expect VFR conditions to prevail across most of the area. The
exception is southeast Missouri and parts of southwest Illinois
where an MVFR cloud deck developed earlier in the day and will
likely persist this afternoon into the evening. Heavy
thunderstorms are expected to develop over the southeast Plains
later this afternoon and move northeast into Missouri and Illinois
this evening. Guidance suggest that the thunderstorms will move
from southwest Missouri into east central Missouri sometime
between23-02Z...and may bypass central Missouri
altogether...however cannot totally rule out storms in central
Missouri at this time. Storms should be exiting the forecast area
into eastern Illinois between 08-10Z. Another round of showers and
a few storms is possible on Saturday...mainly over Illinois.
SPECIFICS FOR KSTL:
VFR flight conditions and some isolated showers are expected to
prevail at Lambert through the afternoon. A wave of heavy
thunderstorms which will bring MVFR and possibly IFR cigs/vsbys to
Lambert is expected between 02-05Z. Lingering rain showers may
continue to impact the terminal through 08-10Z. Ceilings should
lift Saturday morning, but not very confident in timing at this
.PRELIMINARY POINT TEMPS/POPS...
Saint Louis 58 70 40 47 / 80 40 20 30
Quincy 56 64 37 41 / 50 40 30 40
Columbia 52 61 35 41 / 60 20 20 40
Jefferson City 52 61 36 42 / 60 20 20 40
Salem 59 71 42 50 / 80 40 40 30
Farmington 57 68 37 46 / 90 30 20 20
Area Forecast Discussion
National Weather Service Nashville TN
641 PM CDT Fri Apr 13 2018
FOR 00Z AVIATION DISCUSSION.
Model spread has improved slightly in regards to precip amounts
for Saturday, but have some localized areas they highlight
individually. The upper low is currently over the central Plains,
and remains very strong. It looks to intensify slightly overnight,
and remain a closed low for the duration of its impacts on the mid
state. Early chances for precip will move in just after midnight
and spread eastward across the I-65 corridor before 12Z. A few
short term models such as the NAM want to place the first wave of
heavy rain in the northwest zones, while model consensus has
mainly a half inch up to an inch west of I-65 by 18Z. Thats
supported by PWAT values above 1.5 inches for that area during the
morning hours, as well as a 50-60 knot LLJ through the morning
hours as well.
Getting into the early afternoon hours, most models and
especially short term models have a bit of a break in regards to
heavy precipitation. The first initial shortwave that will bring
heavy rain to western zones will weaken slightly and move
northeast out of the area. However, by mid afternoon onward, a
second shortwave develops as the cold front moves eastward across
the MS River Valley. It`s during this time that heavy
precipitation will begin to ramp up again, as well as the time for
best chances for severe storms. Model consensus puts 500-1000
J/kg of MLCAPE as well as 40-60 knots of deep layer shear. A few
models even hint at MUCAPE getting near 1500 J/Kg as well. PWAT
values remain at or above 1.5 inches across the area, and with the
upper low/cold front approaching, the LLJ will increase in speed
to 60 knots over the area. All of these indicators point to the
potential for some strong to severe cells embedded within a line
of storms that could put out some damaging winds. With 0-1km shear
at 30 knots, and even 0-3km helicity around 300-400 m2/s2,
isolated tornadoes can not be ruled out, but main focus for any
stronger cells will be damaging wind gusts.
Towards the late afternoon and into the evening hours, both the
NAM and GFS indicate a slight break in the LLJ over the mid state.
This looks to create an area of convergence over the area ahead
of the front, and looks to help rain development along and east of
I-65. As these storms develop and train over eastern zones,
rainfall totals look to hit the 1-2 inch range just from the late
afternoon into the early morning hours Sunday. The severe threat
looks to weaken in the evening with instability decreasing, so
mainly looking at a heavy rain threat for the evening hours for
the mid state along and east of I-65.
By sunrise on Sunday, the area looks to get between 2 to 4 inches,
with the higher precip axis around 3 to 4 inches possible west of
the Plateau and east of I-65. Locally higher amount could be
possible elsewhere across the mid state if training impacts
localized areas, and the frontal progression slows a bit.
Light showers may continue on the backside of the front on Sunday,
and moving east over the Plateau Sunday afternoon. Temperatures
look to cool off into the 30s for lows by Monday morning, and even
getting close to freezing should skies clear earlier in the
overnight hours. The next chance for precip may be on Wednesday as
another upper low moves through the Midwest and drags a cold front
through the area. Amounts look very low as this looks to be a dry
system, so only have slight chance pops in during the day on
Wednesday. Temperatures will cool off again Wednesday night
through Thursday, but ridging moves in ahead of another strong low
for Friday so temperatures will rebound before next weekend.
00Z TAF DISCUSSION.
BNA/MQY/CKV/CSV...Middle Tennessee finds itself in the maritime
tropical sector of a developing low pressure system this evening,
with the onset of showers and storms still hours away. Winds will
remain gusty overnight, but the HRRR doesn`t bring any cells
across the Tennessee River until just before 12Z. So will bring
this line of storms with a broad area of rain behind the initial
line of cells from west to east during the morning. Ceilings will
drop to MVFR several hours after onset of showers.
Area Forecast Discussion
National Weather Service Tucson AZ
247 PM MST Fri Apr 13 2018
.SYNOPSIS...Gusty winds this afternoon will diminish overnight.
Freezing temperatures are likely late tonight and Saturday morning
for the coldest eastern and southern valleys. High pressure will
bring a rapid warming trend over the weekend before another system
brings gusty winds to the area Monday afternoon followed by yet
another windy system late next week.
.DISCUSSION...Today`s trends continue with cooler and drier air
in place. Our temperature trends are down 15-20 degrees compared
to yesterday. Dew point changes are even more impressive; down
between 30 and 40 degrees which puts them below zero. Winds are
not as strong in most locations, but strong enough when added to
the very dry air mass to yield critical fire weather conditions.
Colder temperatures tonight with lows bottoming out between 5 and
15 degrees below average. One problem will be winds. They will
drop off overnight, but could still be strong enough in some
valley locations to keep the atmosphere mixed, which would
moderate overnight lows. Latest HRRR trends go light and variable
in some colder valley locations including Sulphur Springs Valley
and San Pedro River Valley (much of Cochise and portions of
Graham county). We converted those areas and portions of Santa
Cruz county northeast of Nogales to a warning. far southeast Pinal
and areas west of Nogales were dropped, with winds staying a
little stronger and keeping things mixed. If winds stay about 1 to
3 mph stronger than our current forecast, then the warning areas
may miss out too.
A rapid warmup over the weekend with high pressure building in
from the west. The active higher energy pattern will continue
with another system pushing through the region north of us Monday,
but not as deep as this system. Gusty winds again the main story.
A stronger and deeper system may impact the area later next week.
That one also looks pretty windy, but likely dry this far south.
.AVIATION...Valid through 15/00Z.
Mostly clear. SFC wind wly/nwly at 15-25 kts and gusts between
35-40 kts in most locations thru the early evening hours tonight.
SFC wind slowly diminishing aft 14/03Z with normal trends
Saturday, generally less than 10kts. Aviation discussion not
updated for TAF amendments.
.FIRE WEATHER...Strong winds will continue across the area today on
the backside of an exiting system. Even though it`s much cooler,
the air mass is extremely dry with dewpoints dropping below zero
in many areas. A Red Flag Warning remains in effect through 7 pm
MST this evening.
Saturday and Sunday will be relatively quiet wind-wise as an
upper level ridge builds over the area. The air mass will remain
very dry with minimum RHs in the single digits and poor overnight
Another storm system will likely bring areas of critical fire
weather conditions to portions of southeast Arizona Monday, followed
by lighter, but still breezy winds Tuesday and Wednesday. Yet
another storm system is expected late next week.
Red Flag Warning until 7 PM MST this evening for AZZ150>153.
Freeze Warning from 2 AM to 9 AM MST Saturday for AZZ503-507>509.
Wind Advisory until 7 PM MST this evening for AZZ507>509.
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