Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/29/17
Area Forecast Discussion
National Weather Service Bismarck ND
928 PM CDT Fri Apr 28 2017
Issued at 926 PM CDT Fri Apr 28 2017
Current forecast looks good. No changes needed.
UPDATE Issued at 628 PM CDT Fri Apr 28 2017
High pressure extending from central Manitoba south into North
Dakota will keep skies mainly clear and the weather quiet tonight.
Current forecast looks good.
.SHORT TERM...(This evening through Saturday)
Issued at 319 PM CDT Fri Apr 28 2017
Currently, surface high pressure extended from the Canadian Prairies
into the Dakotas, with low pressure over Hudson Bay and another low
over the 4-Corners area affecting the Front Range and central Plains
states. A weak upper level shortwave low was noted over southern
The weak surface high will weaken and move east slowly tonight, and
the surface wind flow will change from north/northeast today to
southerly on Saturday. The very dry airmass over ND, represented by
surface dewpoints ranging from 5F to around 20F this afternoon,
along with mainly clear skies tonight will allow temperatures to
drop into the 20s once again. We may again drop into the teens in
some locales, but we should be in the 20s most areas.
Mostly sunny and a bit warmer on Saturday with highs from the mid
50s to lower 60s. Noted the HRRR high res model indicating much
lower relative humidity again for much of western and central ND.
Thus attempted to match the 12z HRRR model run for afternoon
relative humidities...with ranges from 15% to around 25% for much of
our area. Luckily south to southwest winds should remain below 15
mph for the most part, and there should not be any fire weather
issues. Went a tad higher for afternoon highs as nam and gfs based
guidance was a bit higher than the blends...and seeing a bit warmer
conditions today with the same airmass in place tomorrow.
.LONG TERM...(Saturday night through Friday)
Issued at 319 PM CDT Fri Apr 28 2017
Mild, but seasonably cool weather is still forecast for Sunday
through Wednesday, with highs in the mid 50s to lower 60s. Then a
warmer end of the week in store for Thursday and Friday with highs
in the 60s. A chance of precipitation also remains for the early to
middle part of next week.
The 12z global model runs were consistent with yesterday`s runs with
development of the larger 4-Corners area system mentioned in the
short term portion. The models develop the low eastward into the
southern Plains Sunday, lifting northeastward to Iowa by daybreak
Monday and into the Great Lakes Monday night/Tuesday. This scenario
would have the precipitation shield clipping eastern North Dakota
with mainly rain - but any westward movement of the track could
affect parts of central ND, especially the James Valley.
Meanwhile another shortwave in the northwest flow aloft ejects out
of southern Alberta Sunday and moves across ND Monday, bringing a
chance of light rain to western and central ND from this secondary
system on Monday. Another shortwave in the northwest flow aloft will
also bring a chance of light rain to our area Tuesday, followed by
another weak wave Wednesday.
For the end of the week, a western upper level ridge builds into the
Front Range and northern Plains, for a dry and warmer end to the
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 628 PM CDT Fri Apr 28 2017
High pressure will maintain VFR conditions across the state
tonight and Saturday.
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1159 PM EDT Fri Apr 28 2017
Late evening observations continue to suggest the main area of
showers will remain to the north and south of the SE Michigan area
with just minimal shower coverage before activity exits eastward by
sunrise. There remains a short time window for MVFR ceiling confined
to locations south of FNT as the remnants of the central Great Lakes
trough merge with the Ohio Valley front. A rising ceiling trend will
then be aided by dry air arriving on wind becoming moderate
northeast from high pressure building over the northern Great Lakes.
Low pressure will concurrently move from Texas along the Ohio Valley
front and bring the next round of rain to our region spreading from
Ohio border northward through the day.
For DTW... Light showers will brush the terminal from the northern
fringes of the Ohio Valley front during the morning before sunrise.
Meanwhile, the central Great Lakes front will wash out and merge
with the Ohio front, and may produce a short period of MVFR ceiling
in the process. The main concern will be the wind turning northeast
by sunrise and becoming moderate in speed through the day which will
likely direct NE traffic flow operations.
//DTW THRESHOLD PROBABILITIES...
* Moderate confidence for ceilings 5000 ft or less through the
morning and again Saturday night.
Issued at 1055 PM EDT Fri Apr 28 2017
An interesting set up this evening as a double barrel frontal
structure is supported by a broad 130 knot level jet. The resulting
complex frontal circulations resulted in surface based convection
along the primary front over the Ohio Valley and a broad band of
ordinary showers to the north of the trough/front over the central
Great Lakes. Weaker showers on the fringes of these areas has
brushed SE Michigan during the evening with an occasional pocket
developing overhead and moving quickly eastward. All of this
continues to battle dry air in the low levels, mainly below about 750
mb with the end result being scattered light rain showers across the
area. The same general pattern will continue through the night
before a diminishing trend is forced mainly by the short wave ridge
building into the Midwest and Great Lakes ahead of the large system
digging into Texas. The relative break in the action will last
through the morning before a renewed surge of moisture develops
through the rest of Saturday.
Issued at 320 PM EDT Fri Apr 28 2017
12Z DTX sounding revealed an 850 mb dew pt depression of 31 C, with
PW value of 0.42 inches. None-the-less, looks like there will be
just enough isentropic ascent (295 K) and moisture advection
working through southeast Michigan (mainly south of M-59) this
evening/overnight to support some light showers based on latest
satellite/radar trends and hi-res solutions of HRRR and Rap13.
Negative LI`s stay south of the border, and left thunder mention
out. Surface cold front sinking south and exiting jet forcing up
north will also support chance/scatter pops there.
Latest water vapor imagery shows highly amplified upper level
pattern over North America, with longwave trough over the Rockies
and excellent upper level jet energy tracking into Four Corners
A convergence of Pacific Moisture/Pineapple connection, coupled with
the Gulf of Mexico/Caribbean moisture as large Bermuda High will
remain in place through the weekend, drawing flooding concerns by
Monday as large and powerful 500 MB low develops over the Central
Conus over the weekend. The system will be lifting northeast into
the Midwest (Iowa) by Monday Morning.
Moisture parameters will be record/near record for end of
April/start of May this far north, as 700 mb dew pts approach 5 C
toward Monday morning, nearing tropical status, with 850 mb dew pts
equally impressive checking in between 13-15 C. With sufficient
destabilization/convective elements, showalter index going slightly
negative and deep warm cloud layer, several inches of rainfall is
certainly possible for the second half of the Weekend into Monday,
which will create flood concerns. Unfortunately, placement of heavy
rain axis remains difficult, but good low level FGEN/isentropic
ascent will be established by Sunday, as strong high (1032-1034 MB)
remains parked over/near James Bay. Do think the surface warm front
will not clear much past the southern Michigan border during the day
on Sunday (Lake Erie influence), which should help showers persist
even in southern areas, but max mid level forcing does appear to be
lining up across northern sections of the CWA into northern lower
Michigan Sunday Night.
As of right now, it appears the robust max 6HR height fall center
will already be over Central Great Lakes Monday afternoon, thus
strong cold frontal/occlusion passage with good upper level support
will occur early in the day. Moisture/instability axis passing east
by around NOON, helping to mitigate any severe threat. Still not out
of the woods Sunday night with 65 knot jet at 850 MB, but meager
lapse rates within the moist airmass should be hindrance. Bottom-
line, Heavy rain remains the biggest concern, and flood watch will
likely be needed for the second half of the weekend.
Lingering precipitation and gusty conditions will be possible Monday
evening into Tuesday afternoon as low pressure travels northeast
from Wisconsin into the Upper Peninsula. Cooler air that is expected
to wrap around the low and push into Michigan throughout Monday
afternoon will help to increase stability, minimizing the chance for
thunderstorms, as conditions remain breezy. The low pressure system
will continue to push northeast through Quebec late Tuesday into
Wednesday, as a surface high edges eastward across the Great Lakes
region. This will act to keep us dry and will keep winds light
through the middle of the week, as temperatures remain moderate with
daytime highs capped in the mid-50s.
The next chance for rain will return Thursday into Friday as a warm
front slowly pushes north into the MI/OH border. The GEM model run
suggests that the warm front will protrude into Michigan, allowing
rain showers to fall over our southern counties that border Ohio,
however, several other long-range models hold the rain south of
Michigan through the end of the week.
Gusty southwesterly winds over the morning will slowly continue to
diminish this afternoon. Relatively light winds are then expected
by early tonight before strong high pressure builds into Ontario and
low pressure begins to organize over the plains. This will bring an
increase in north/northeast winds to the marine areas and
potentially allowing waves to build high enough to warrant a Small
Craft Advisory for nearshore waters of Lake Huron and Saginaw Bay.
Monday will then see wave heights decreasing as southerly winds take
over ahead of a cold front. However, winds will once again gust up
to 30 knots. As the low approaches the Great Lakes region this
weekend, an increasingly unsettled, wet pattern will set up.
Thunderstorms will also be possible Sunday into Monday.
Lake Huron...Small Craft Advisory from 3 AM Saturday to 6 AM EDT Monday for
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Quad Cities IA IL
652 PM CDT Fri Apr 28 2017
...00z AVIATION UPDATE...
Issued at 313 PM CDT Fri Apr 28 2017
18Z surface data has a frontal boundary from central Kansas into
northwest Indiana. Dew points were in the 20s and 30s from the Great
Lakes into the northern Plains. South of the front dew points were
in the 50s and 60s.
.SHORT TERM...(This Evening through Saturday)
ISSUED AT 313 PM CDT Fri Apr 28 2017
Current radar trends show a period of dry weather late this
afternoon across the southeast half of the area.
This evening, the rain across the northwest half of the area will
end but spotty light rain or drizzle will persist or move into the
area from the southwest.
After midnight, the question becomes how quickly will the atmosphere
re-saturate under the persistent northeast flow off the lake. The
current forecast has light rain moving back into the southern half
of the area prior to sunrise. However, if the depth of the dry air
is deeper than what the models depict, like today, then most areas
south of I-80 could remain dry until sunrise Saturday.
On Saturday, the first part of the main storm system moves into the
area. Strong northeast flow will be seen across the area with rain
overspreading the area during the morning. As lift increases in the
late morning and afternoon hours, some embedded thunderstorms are
expected to develop which will increase rainfall amounts across the
southeast half of the area.
The combination of clouds, rain, and northeast winds on Saturday
will keep nearly all of the area in the 40s. The possible exception
is south of a Galesburg, IL to Kahoka, MO line were temperatures may
get just above 50 degrees.
.LONG TERM...(Saturday Night through Friday)
ISSUED AT 313 PM CDT Fri Apr 28 2017
Model trends remain fairly consistent, lending increased confidence
to active weather through the weekend, featuring heavy rain,
resulting river flooding and isolated short term flooding, and
possibly a window of severe storms. Long term river flooding is
discussed in detail below.
Synoptic models still favor the southeast third of the forecast area
for the heaviest rain axis, on the order of 3 to 4 inches. By
Saturday night into Sunday, increasingly moist soils will make
conditions prime for localized flash flooding from rain swollen
creeks, streams and ditches. Heavy rainfall rates could also produce
some significant street flooding. Most synoptic and convective
allowing models support some potential for severe weather Sunday
afternoon and evening as a surface low and warm front lift north
through the area. There are still disagreements in the eventual path
and timing of the low, but it is becoming increasingly clear that at
least some portion of the forecast area, especially the southeast,
will be at risk. Would not be surprised to see an upgrade from
marginal to slight risk, at least in the south. Clouds may limit the
amount of destabilization and areal coverage of severe storms, but
even a modest amount of MUCAPE would support a QLCS wind/tornado
threat given the strong shear and favorably aligned 0-3km shear
For Monday, a well-developed TROWAL will sustain lingering showers,
with afternoon temps struggling to get out of the 40s. Tuesday
through Friday, expect mainly quiet weather with near to slightly
below normal temperatures.
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
ISSUED AT 643 PM CDT Fri Apr 28 2017
Light rain along/n of I-80 will taper off this eve with exiting
upper level wave, with some patchy drizzle lingering along with
mvfr to local ifr conditions this evening. Overnight, I went with
hrrr cig height trends which are verifying well and show gradual
improvement to vfr all sites but BRL where kept mvfr conditions.
On Saturday, anticipate next round of rain aided by isentropic
ascent to overspread the terminals by mid morning through midday
with conditions lowering to mvfr with pockets of ifr possible.
Winds will remain northeasterly throughout the taf cycle at around
10-15 kts and turn gusty on Saturday.
Issued at 1141 AM CDT Fri Apr 28 2017
Updated morning forecast guidance from the North Central River
Forecast Center now includes 72 hrs of QPF, through the bulk of
the heavy rain event for the forecast area. Confidence is
increasing on the potential for widespread heavy rain through the
period. Parts of west central and northwest Illinois remain
favored for the heaviest amounts, potentially 2 to 3 inches and
These amounts place the Illinois tribs and the Mississippi River
south of the Quad Cities at the most risk of significant flooding.
Moderate flooding is possible into next week on the Rock River,
as well as the La Moine River, and the mainstem Mississippi from
New Boston to Burlington. Other faster responding points in
eastern Iowa will also be watched closely this weekend.
There is still some uncertainty on the axis of heavy rain, and those
with interests along area rivers, streams and creeks should check
back for updates through the weekend.
LONG TERM...RP Kinney
Area Forecast Discussion
National Weather Service Wilmington NC
956 PM EDT Fri Apr 28 2017
High pressure will extend across the area from offshore through
Sunday. Expect warm temperatures and isolated sea breeze
showers or storms, mainly Sunday. The next cold front will
bring a chance of showers and thunderstorms late Monday into
early Tuesday. High pressure will follow for the mid-week
period. Low pressure system may impact the region during
Thursday with a soaking rain.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 1000 PM Friday...It`s been fascinating watching the low
clouds along the coast on 11-3.9 micron satellite imagery this
evening. Low clouds from Myrtle Beach northward appear to
eroding along the south edge, but clouds in the Georgetown
vicinity are holding together a little better. Not even the HRRR
model is good enough to forecast the movement of such a small
mesoscale phenomenon, so I`ve attempted to manually extrapolate
the cloud movement northward in the forecast grids over the
next 4-6 hours as they spread inland but spare the immediate
Cape Fear coastline. No significant changes to forecast low
temperatures. Discussion from 630 PM follows...
An unbelievably humid airmass for this early in the year covers
the Carolinas. Dewpoints in the mid 70s are practically unheard
of in April, and even with nearshore ocean water temperatures
near record warm territory these dewpoints have generated areas
of sea stratus and even sea fog earlier along the GA and SC
Inland cumulus should die away fairly quickly this evening with
the loss of daytime heating. It`s a little more uncertain how
clouds will respond near the coast: very humid air streaming
onshore will experience frictional/speed convergence which
could maintain a very low stratocumulus deck affecting
Georgetown, Myrtle Beach, and Wilmington through the evening
hours. Precipitation appears unlikely overnight as the depth of
our moisture is very limited and will be capped off by warm and
very dry air aloft.
Lows tonight will run at least 15 degrees above normal for the
date with 69-74 expected, coolest inland.
Climate note: Wilmington`s low temperature so far today has been
74 degrees. Assuming we don`t drop below 74 between now and
midnight standard time (1 AM daylight time) this will establish
a new all-time record warm low temperature for the month of
April in Wilmington. Records extend back to the year 1874.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY NIGHT/...
Saturday and Sunday: The synoptic pattern will be dominated by deep
layered subtropical ridging with the region positioned just to the
west of the 850-500 hPa anticyclone. Modified forecast soundings for
both Saturday and Sunday show pronounced capping with only the far
interior west of I-95 becoming uncapped for about 1-2 hours with the
sea breeze. Given lower tropospheric moisture looks pretty meager
outside of the boundary layer, prefer to go with a dry forecast for
both days. Temperatures will remain above normal with highs ranging
form the lower 90s well inland to around 80 at the beaches. Lows
Sunday morning will range from the upper 60s inland to the lower 70s
at the beaches.
Monday: A cold front will approach from the west Monday as high
pressure shifts farther offshore and a powerful storm system moves
into the upper Mississippi Valley. Moisture return ahead of the
front looks solid with taps noted from off the Gulf of Mexico and
Atlantic. Although the upper low and the core of the strongest
forcing looks to pass well to the north, there will be enough to
support a broad swath of showers/tstms across the frontal zone. Pops
will be increased to 70% for most zones Monday night as the front
sweeps offshore. Highs will warm into the lower-mid 80s away from
the beaches Monday afternoon with lows Tuesday morning ranging from
the upper 50s well inland to the mid 60s at the beaches.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
Surface and mid level ridge will weaken and drift east Mon,
allowing a cold front to approach from the W. Low pressure and
associated strong dynamics and upper level support will be well
dislocated from the Carolinas as a cold front moves across the
area Mon night. This suggests convection weakening as it moves
into the eastern Carolinas. Current timing brings the likelihood
for showers and thunderstorms later Mon and Mon night.
As the front moves off the coast Tue morning, high pressure
along the Gulf Coast will slide east and then offshore to our S
during Wed. This should bring a dry period. Deep low pressure
will move out of the mid south and Gulf coast states Wed,
lifting slowly to the NE. Its associated cold front will move
into the Southeast states Thu-Thu night, bringing the risk for
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
As of 00Z Saturday...Low confidence forecast with cloud heights
along the coast over the next several hours as we transition
from day to night. Very rich low level moisture streaming
onshore has supported MVFR/IFR ceilings along the coast of the
Carolinas this afternoon. While the moisture will remain
overnight, the loss of daytime heating could cause an erosion
of this cloud cover -- but to what degree is unknown. The last
few visible satellite images show fairly solid low cloud cover
extending from Charleston and Georgetown which should move
northward along the coast now through 06Z. Forecasts are for IFR
ceilings to perhaps improve to MVFR temporarily in the MYR/CRE
area after 02Z, but confidence in low.
At least scattered low clouds below 1000 feet AGL will persist
all night even if ceilings do not develop. Models even suggest
after 06Z enough moisture will push inland that FLO and LBT
could see some scattered low clouds develop. VFR conditions
should develop after daybreak.
Extended outlook...Periods of IFR/MVFR conditions are possible
in showers and thunderstorms late Monday into early Tuesday.
NEAR TERM /THROUGH TONIGHT/...
As of 1000 PM Friday...The seabreeze has died away leaving winds
mainly in the 10-13 knot range which should persist overnight.
No significant changes are needed to the forecast. Discussion
from 630 PM follows...
South winds across the coastal waters have been strongest
nearshore for the afternoon with the seabreeze. Farther offshore
winds are barely 10 knots at the Frying Pan Shoals buoy and the
Edisto buoy east of Charleston. Once the seabreeze dies away
expect a very warm and humid onshore flow to continue overnight.
Although we don`t expect true sea fog to develop, periods of
low stratus clouds and hazy visibilities in the 2-4 mile range
SHORT TERM /SATURDAY THROUGH MONDAY/...
As of 300 PM Friday...Southerly wind regime will persist
through Monday as the region remains along the western flanks of
Atlantic high pressure centered well offshore. Speeds will
generally remain 10-15 kt through the period, except Sunday
Night into Monday where speeds increase to 15-20 kt and 20-25 kt
Monday night as low-level jetting and a tightening pressure
gradient settle in ahead of a cold front. Seas will slowly build
over the weekend, peaking 5-7 ft by Monday night ahead of the
cold front. A Small Craft Advisory could be needed as early as
LONG TERM /TUESDAY THROUGH WEDNESDAY/...
As of 300 PM Friday...In the wake of the cold frontal passage
early Tuesday, offshore winds will slowly diminish. The offshore
trajectories will knock seas down and should drop below Small
Craft Advisory levels by Tuesday afternoon. There are no
concerns for Wednesday into Thursday.
NC...Coastal Flood Advisory until 2 AM EDT Saturday for NCZ107.
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
859 PM CDT Fri Apr 28 2017
859 PM CDT
For Evening Update:
Minor adjustments to going forecast this evening, mainly to refine
pops based on radar trends. Generally, only light showers over
far north/northwest and far south/southeast parts of of the FA
Evening surface analysis depicts a stationary frontal boundary
from southern IL/IN...extending southwest to low pressure over
west Texas. Scattered thunderstorm clusters were occurring along
the front well south of the area this evening. Farther north,
925-850 mb obs indicate an elevated frontal zone from KS into
northwest IL and southern WI. Showers were occurring with a pair
of low-amplitude short wave disturbances, mainly north of and
southeast of the cwa, with a minimal in precip across the forecast
area in a region of weak warm/moist advection and isentropic
ascent though with little forcing. 3km WRF and HRRR seem to be
capturing the general character of the precip fields and trends,
which suggest maintaining some low-chance pops for some spotty
light rain across the far north and far south parts of the area
this evening. Guidance does depict a sheared mid-level wave
approaching from the southwest toward morning which looks to
increase precip potential across the southern tier or two of WFO
LOT counties toward sunrise, but otherwise little in the way of
significant rainfall is expected overnight.
Most guidance is in good agreement in spreading rainfall northeast
across the forecast area mid-late Saturday morning, with another
low-amplitude short wave rippling along the elevated baroclinic
zone across the area. Will have to watch convective development
north of the surface front overnight however, which may tend to
block some of the stronger moisture transport into northern IL and
IN. Stout northeast winds develop by early Saturday as well, which
will also work to maintain a feed of drier low level air into the
region. While periods of rain on Saturday are a good bet, these
factors may help initially reduce heavy rainfall threat somewhat.
305 PM CDT
Concerns through Saturday are with moderate to potentially heavy
rainfall beginning Saturday afternoon. A Flash Flood Watch has
been issued from Saturday afternoon through the rest of the
Light rain has struggled to become widespread across the area
with this initial mid-level disturbance and start to isentropic
ascent, due to weak forcing for lift and inherent low-level dry
air. Spotty light showers should continue through early evening,
with likely a wedge in the central CWA with little to no rain.
As gradual cyclogenesis occurs across the southern Plains tonight,
the synoptic boundary (initial warm front) that is located just
north of I-80, will start to collapse southward with northeast
winds slowly increasing. While a spotty light shower or two
through the rest of tonight cannot be ruled out, a general lull in
forcing is expected with focus well to the southwest of the
As the frontal zone to the south develops warm frontal
characteristics on Saturday morning, it will start to slowly
progress northward. The low-level northeast flow will initially be
problematic for rain, but this should be overcome from south-to-
north during the afternoon. Just how quickly this occurs will
hinge heavily on amount of convection to the south robbing
moisture transport. If slower, rain may not begin in the far north
until late day or even early evening. Confidence in rainfall
amounts for Saturday afternoon is somewhat low, especially the
northern half of the CWA, and it could end up being lower during
251 PM CDT
Saturday night through Friday...
The potential for copious amounts of rain still exists for Saturday
night in particular, and continuing into Sunday. However, still have
concerns that convection to our south will result in less moisture
and rainfall than the models are currently predicting. While models
may be too high on specific precipitation forecasts, still have
enough confidence to go with a Flash Flood Watch for areas along and
east of the I-55 corridor Saturday afternoon through Sunday night.
Saturday night...The surface low organizes over southeast Missouri
with its warm front remaining just south of the forecast area.
Expecting moisture to pool across central and northern IL and
northwest IN, mainly along and east of I-55. However, have serious
concerns about how much moisture will actually pool in this area.
Convection to the south may hog some of the forecasted moisture
leading to less moisture/rainfall than forecast. Current forecasts
feature 1.5 to around 1.8 inches of PWAT, well above normal for this
time of year. Given my concerns, went with lower forecasted rainfall
than many of the models would suggest. Either way, expecting
widespread rainfall across the region Saturday night. Will keep a
chance of embedded thunder in the forecast since the saturated
soundings still feature a little elevated CAPE. Thinking the better
coverage of thunderstorms will be also along and east of I-55, but
will keep a chance along and south of I-88.
Sunday...Rain continues as the warm front lifts north to either the
I-80 to I-88 corridor. PWAT values are still forecast to remain over
1.5 inches so the threat of heavy rain will continue. Agree with
SPC`s Day 3 outlook for our area. Have low confidence in severe
storm coverage and strength because I am unsure how well and quickly
the atmosphere will recover from Saturday night`s rainfall. In
addition, cloud cover may limit CAPE values. If we get get breaks
in sun and are able to recover, strong to severe storms are
expected. Shear values will be 60-80 kt. CAPE values will likely be
highest south of I-80 and forecast values range from 500-1000 J/kg
in the GFS to 1000-2000 J/kg in the typically overly aggressive NAM.
Therefore, will lean more toward the GFS` solution.
If strong to severe storms form, expecting discrete storms. Severity
of threats will depend on how much CAPE we have to work with, but
all severe types and flooding are possible with the storms.
Have low confidence in high temps Sunday as any breaks in clouds
will likely lead to higher temperatures than forecast especially
south of the warm front.
The low`s cold front moves through Sunday evening and night and
expecting storms to consolidate along the front leading to
Monday through Friday...
Cooler air arrives with the upper level trough early next week
leading to highs in the 50s most of next week. Light wrap around
showers are expected Monday as the upper level low rotates over the
region. While we do not need more rain, rainfall amounts should be
minimal. Monday also looks gusty with southwest winds gusting to
around 30-35 MPH.
Rain finally moves out and high pressure moves in Tuesday, and we
may even see a little sunshine! The high should keep rainfall
associated with the next low off to our southeast, but the GFS has
the precip clipping the southeast corner of the forecast area. Have
low confidence in whether the showers will reach the forecast area
For the 00Z TAFs...
Period of MVFR cigs expected this evening with potential for some
lifting of cigs back to VFR later tonight as some drier low level
air advects in from the northeast. First, wave of rain is expected
to move into the area midday Saturday with cigs likely quickly
falling back to MVFR. Steadiest moderate rain expected Saturday
afternoon with some abatement in the rain looking possible toward
evening and continuing into Saturday evening. Cigs expected to
continue to fall to IFR Saturday evening with some drizzle or
light rain possible. Northeast winds will begin to pick up late
tonight, but should grow increasingly strong and gusty Saturday,
with occasional gusts around 30kt by afternoon and continuing into
251 PM CDT
Headlines...Will continue the Small Craft Advisory for late tonight
into Sunday afternoon. While gales are possible over the southern
half of the lake Saturday evening, I think it will be a brief 5 hour
window that will not need a watch at this point. However, I did have
enough confidence to issue a gale watch for the northern half of the
lake Sunday afternoon into Monday morning.
Weak high pressure shifts southeast this evening and winds become
north to northeast. Winds increase as the gradient tightens between
a high building over south central Canada and low pressure taking
shape over the southern plains. Guidance differs on whether the
gradient will be strong enough to support low end gales over the
southern end of the lake Saturday afternoon and evening.
As the low shifts north to Iowa Sunday afternoon, the area of
stronger winds also shifts north. Have higher confidence in gales
occurring over the northern end of the lake Sunday afternoon into
Monday morning, so decided to go with a gale watch. The low moves
over the northern end of the lake late Monday night/early Tuesday
morning along with the low`s cold front. Winds become west behind
the front with at least 30 kt expected. Another Small Craft Advisory
will likely be needed Monday and Tuesday. There is a chance that low
end gales may occur over the southern half of the lake but
confidence is medium-low given differences in model solutions.
The low continues to Quebec Tuesday night followed by high pressure
building over the lake Wednesday night into Thursday.
IL...Flash Flood Watch...ILZ014-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
ILZ039...1 PM Saturday to 7 AM Monday.
IN...Flash Flood Watch...INZ001-INZ002-INZ010-INZ011-INZ019...1 PM
Saturday to 7 AM Monday.
LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...4 AM Saturday to 4 PM Sunday.
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Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
932 PM CDT Fri Apr 28 2017
Issued at 932 PM CDT Fri Apr 28 2017
Two surface frontal boundaries exist over our region this evening.
The northern one extends from near Chicago southwestward to
Quincy and to near Sedalia. This has not moved much over the past
few hours and if CAA and pressure rise trends are any indication,
is undergoing frontolysis and will dissolve soon. The second
frontal boundary is southeast of our CWA and extends from just
north of Evansville, IN to just south of Cape Girardeau to near
Poplar Bluff. It is this front that will soon become the main
front as its northern cousin dissipates.
The 00z NAM as well as the various iterations of the HRRR models
continue to support the instability axis across southern MO and
far southern IL. While thunderstorm coverage, currently growing in
southeast MO and southern IL, will continue to increase and
expand northward, it is over the nearly stationary instability
axis in the southern CWA where the greatest threat for excessive
rain will be along with an isolated severe storm which will
probably tend to favor hail as the primary severe threat.
The northward expansion of the pcpn later tonight will be
courtesy of the southern front (by this time...just "the front")
buckling back to the northwest in response to a strong low
pressure wave approaching from the southwest. It is how far this
front buckles back to the northwest which will decide how this
forecast evolves on Saturday, particularly in the afternoon and
evening. Current model depictions generally favor the front
getting thru STL metro, but not much more, but there remains an
unusually large spread despite this being within a 24hr forecast.
This should enable pcpn to expand into STL metro later tonight and
into much of central MO with little problem, but questionable on
whether it reaches UIN before 12z/Sat. Instability for thunder
will also tend to lag the northward expansion of pcpn.
All in all, the overall forecast remains in play, with increasing
rain chances and main initial flood threat in the south--expanding
northward after daybreak on Saturday.
.SHORT TERM... (Through Late Saturday Afternoon)
Issued at 339 PM CDT Fri Apr 28 2017
Showers and thunderstorms that are ongoing over southwest and
south central IL are occurring in association with a region of
elevated CAPE, and lift via a south-southwesterly LLJ and
migratory impulse in the southwest flow aloft. Present indications
are this activity will continue to move east and exit the CWA
before 00Z in association with continued eastward motion of the
upper level disturbance. Thereafter there may be a rather tranquil
period until late this evening. The wavy warm front currently
extends from western KY through the bootheel curving southwest
through AR into eastern OK. This front is expected to lift slowly
northward and become better defined across the far southern CWA -
southeast MO and southern IL tonight. Late this evening, another
impulse currently located in KS will translate across the region
providing some large scale ascent. More importantly the broad and
stout southwesterly LLJ is expected to result in strong lift along
the broad frontal zone, with the ascent primarily focused along
the front and into the cool sector. This is expected to result in
widespread thunderstorm development from 03-06Z across southern MO
and southern IL. Attendant with these storms will be a threat of
large hail, as well as heavy rainfall/flash flooding giving there
west-east alignment and high rainfall rate and training potential.
The axis of storms and the northward and growing adjoining
stratiform rain region should then gradually spread northward
through the overnight hours with the strongest storms shifting to
the east into the OH Valley region.
A stormy and volatile period is expected on Saturday with potential
for both severe weather as well as heavy rain and flash flooding.
There remains uncertainty in the specifics that we probably won`t be
able to nail down until as we get much closer. The overall scenario
has the mid/upper flow continuing to back and become more south-
southwesterly as the upper low/trof shift across the
southern/central Rockies into the Plains. The next result is the
warm front will lift northward through central/eastern MO and
southern IL during the day as a surface low tracks into eastern OK.
The result will be an expanding unstable warm sector and therefore
risk of surface-based storms with attendant hail and damaging wind
threats. Complicating the whole scenario is an ongoing MCS will move
from western MO and into central MO during the late morning and then
across the remainder of the CWA during the afternoon hours. Current
thinking is that while WAA generated showers and storms will be
possible at just about anytime, this anticipated MCS will re-
energize by afternoon and pose a greater severe weather threat as it
taps the instability of the expanding warm sector. A very moist air
mass with PWs greater than 200% of normal will promote high rainfall
rates and any locations seeing longevity of storms and training will
have a heightened flash flood threat.
.LONG TERM... (Saturday Night through Next Friday)
Issued at 339 PM CDT Fri Apr 28 2017
Saturday night, upper low to continue lifting northeast out of
southern Plains into region, which will begin to lift warm front
back to the north inconjunction with deepening surface low. Strong
low level jet will pull in plenty of moisture, so continue to see
PWs in excess of 1.5 inches, with some models indicating close to
PWs around 2 inches. Will see several rounds of showers and storms
Saturday night through Sunday. Model differences on location of main
axis of highest qpf still a problem with NAM the furthest north.
Will keep superblend solution, which is a bit further north than
yesterday and a bit less than the WPC qpf. As for chances of severe
weather, strong to severe storms possible, especially over east
central/southeast MO and southwestern IL Saturday night.
By Sunday as surface low moves due north over western MO, warm front
to slide north of forecast area, while surface low drags cold front
through region during the afternoon and early evening hours. So dry
slot to move in behind cold front with precipitation tapering off
towards Midnight Sunday. Strong to severe chances look best over
southeast MO and far southern IL.
Storm total qpf still looks to be between 3 and 5 inches with the
highest amounts extending along the I-44 corridor in MO and I-55
corridor in IL. This could lead to a significant hydrologic event
with moderate to major flooding occurring on a number of river
basins. Flash flood watch to remain in effect through 06z Monday,
though have added a few more counties along the northern side of the
Will see wrap around showers on backside of system late Sunday night
through Monday. Beyond that, another brief break in the
precipitation before next system moves Tuesday night through
Thursday night. Extended models having differences in timing and
placement with this system, so went with a blend for now. Otherwise,
coolest temps will be on Monday with highs in the 50 to 60 degree
range, then moderate back into the 60s for the remainder of the
.AVIATION... (For the 00z TAFs through 00z Saturday Evening)
Issued at 652 PM CDT Fri Apr 28 2017
IFR conditions are expected to prevail for the TAF sites for much
of the valid period, especially as a frontal boundary digs in to
the southeast and allows low CIGs to become more widespread and
lower. Rain will increase from the south later tonight and, once
it moves in, will be difficult to completely dislodge from the
area and as a result was very difficult to find a break for the
TAFs. Looks like the best opportunity for a break from the rain
will be for the STL metro sites from late morning until late
afternoon as the frontal boundary lifts northward and should also
allow for an improvement in conditions to MVFR or perhaps VFR.
Surface winds will be NE north of the front and will begin to
become oriented this way this evening and will veer southerly when
the front pushes north thru STL metro later on Saturday. Winds
will also become gusty later tonight and Saturday as the storm
system to the west winds up.
MO...Flash Flood Watch through late Sunday night for Audrain MO-Boone
MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-
Monroe MO-Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds
MO-Saint Charles MO-Saint Francois MO-Saint Louis City MO-
Saint Louis MO-Sainte Genevieve MO-Warren MO-Washington MO.
IL...Flash Flood Watch through late Sunday night for Bond IL-Calhoun
IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
Madison IL-Marion IL-Monroe IL-Montgomery IL-Pike IL-
Randolph IL-Saint Clair IL-Washington IL.
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
936 PM EDT Fri Apr 28 2017
High pressure will persist over Bermuda into Tuesday. A
stationary front will linger over southern Pennsylvania late
tonight through Saturday before lifting north Sunday. A
stronger cold front will move across the region from the west
Monday night. Canadian high pressure will then build over the
area through the midweek.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
As of 9pm, low pressure is over the Big Bend region of Texas
with a warm/stationary front extending NE across the Ohio valley
and reaching the eastern West Virginia panhandle. Severe
convective storms have developed on the north side of this front
along the Ohio River valley and will move northeast through the
night. Instability increases and bulk shear remains high through
the night. This should allow strong to possibly locally severe
thunderstorms to move along this front late tonight. This puts
the northern third of the CWA at risk. Height rises associated
with warm air advection should make the activity elevated with
hail as the primary threat.
SPC has expanded the marginal risk for this area and our
hazardous weather outlook mentions this threat for this area as
well. This will continue to be monitored through the night. 00Z
HRRR continues recent trend of perhaps two rounds of convection,
one late tonight and the second toward daybreak. This is
climatologically the minimum in thunderstorm activity, but not
Lows primarily in the 60s, but the cities may not drop below 70.
This has never happened before in DC (in April) - record high
min is 69 set in 1896.
The year 1896 holds the record high min for Baltimore for five
consecutive nights in April. They dropped only to 70 on April
See climate section for more information.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
"Hot" will be the operative word for Saturday as high pressure
moves off the southeast coast and pumps warm air into the Mid
Atlantic. Again, see the climate section below for high
temperature records - these will definitely be in jeopardy. Heat
indices will be in the low/mid 90s in the I-95 corridor, nowhere
near heat advisory levels but notable for April.
Continued warm temperatures Saturday night/Sunday. There is not
any real trigger for organized convection approaching, but this
is somewhat of a summertime pattern. Hence it is not out of line
to see orographically driven storms develop Sunday afternoon.
The best thunderstorm chances hold off until Monday.
.LONG TERM /MONDAY THROUGH FRIDAY/...
A cold front over the eastern Ohio Valley early Monday will move
across the region Monday into Monday night. Showers and
thunderstorms, some strong, will develop ahead of and along the cold
front Monday afternoon and evening. Temperatures will be about 15
degrees above normal.
Weak high pressure will build in behind the cold front Tuesday. A
gusty westerly breeze will usher in drier air. Temperatures will not
be as warm as Monday, but could still be 5 to 10 degrees above
As the high moves east, a secondary cold front will move across the
region from the northwest Tuesday night. This front should be a dry
front. The front could sag into the Carolinas Tuesday night before
starting to move northward as a warm front on Wednesday.
A low pressure system is expected to develop along the western end
of the warm front over the Lower Mississippi Valley Wednesday night
and early Thursday. We introduce a slight chance of showers or a
rumble of thunder Wednesday night with a higher chance to likelihood
of encountering showers and thunderstorm Thursday through
At the tail-end of an associated cold front with the storm system,
another storm system could develop and deepen over the interior
Southeast U.S. Friday and Friday night. The chance of showers and
thunderstorms will linger during the period. Temperatures will also
be closer to normal Friday and Friday night.
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions prevail tonight through Sunday night. A few
thunderstorms possible overnight with MRB being the main
consideration though VCTS for IAD and BWI/MTN were also
Ifr to lifr conditions possible Monday and Monday night from
thunderstorms associated with a strong cold front moving through.
Vfr conditions Tuesday and Tuesday night. Winds south-
southwest 10 to 15 knots Monday, becoming southwest around 10
knots Monday night, then west- southwest 10 to 15 knots Tuesday,
and west 5 to 10 knots Tuesday night.
Light southerly flow, below SCA values, tonight through
Saturday night. Isolated thunderstorms possible on the northern
part of the Bay late tonight into Saturday and on all of the
Small craft advisories likely Monday as south winds increase
ahead of a cold front Monday night. Small craft advisories
possible Monday night and Tuesday with the frontal passage. No
marine hazards Tuesday night. Winds south 10 to 20 knots gusts
25 knots Monday, becoming southwest 10 knots Monday night, then
west- southwest 10 to 15 knots Tuesday, and west 10 knots
Tidal anamolies are expected to decrease slightly over the next
several days as wind flow decreases. However, return of southerly
flow later today into the weekend will keep anamolies elevated.
Record highs/warm lows through the weekend:
Saturday 29 April...91 (in 1974)/68 (in 1956)
Sunday 30 April...92 (in 1942)/67 (in 1983)
Saturday 29 April...91 (in 1974)/67 (in 1956)
Sunday 30 April...92 (in 1910)/63 (in 1983)
Saturday 29 April...87 (in 1996)/62 (in 1996)
Sunday 30 April...86 (in 2007)/64 (in 1983)
Area Forecast Discussion...UPDATED
National Weather Service Little Rock AR
610 PM CDT Fri Apr 28 2017
Updated to include the 00Z aviation discussion below...
A warm front remains across the state early this Fri
evening...with some MVFR CIGs ongoing at the NRN terminals. Along
and south of this front...VFR conditions are ongoing. As time goes
on this evening...some SHRA/TSRA will become possible along and
south of this front early in the period. Then as the front lifts
north...expect the chances for SHRA/TSRA to shift north as
well...giving the central/SRN terminals a break. NRN terminals
will see some precip chances remain through most of this TAF
period. Chances for precip will return for the central/SRN
terminals by late morning/early afternoon Sat.
.PREV DISCUSSION...(ISSUED 250 PM CDT Fri Apr 28 2017)
SHORT TERM...Tonight Through Sunday
There haven`t been any significant changes made to the going
forecast. The initial onslaught of heavy rain is forecast to begin
tonight as the warm front lifts into northern Arkansas, with
convection along the stalled boundary continuing through the day
Saturday. Eventually as the upper support well to the west of
Arkansas shifts east into the southern plains tonight and Saturday
the cold front with this system will get legs and move east into
the state. This would be primarily tomorrow evening and into the
overnight hours Saturday night.
There remains some uncertainty with regard to rainfall amounts and
severe weather chances. First, the warm front has been forecast to
shift into northern Arkansas this afternoon and evening, with
convective initiation late this evening in the northwest parts of
the state before spreading across all of northern Arkansas during
the nighttime hours. There is some indication that the front will
remain hung up in the Ouachitas this afternoon and that convective
initiation will occur in the western parts of the state before
shifting north tonight. If this occurs, model soundings are
supportive of very strong updrafts with the potential for large
hail, damaging winds, and even a tornadic threat. Only time will
tell, but the GFS as well as the convection-allowing HRRR indicate
this will be a possibility. Otherwise the remainder of this event
seems fairly straight forward, with the main opportunity of heavy
rains and severe weather being along/ahead of the cold front as it
moves through tomorrow.
Regarding rainfall, totals have been trimmed back slightly, but
storm total amounts in excess of 5" seem very likely across
northern and northwestern Arkansas. Given the convection aspect of
this event, I would not be surprised to see some rainfall totals
in the +7-8" range pop up in the Ozarks, but this will be more of
an exception. Given the setup, especially given the near-record
PWAT values forecast with the stronger forcing along the cold
front tomorrow evening, flash flooding and river flooding still
seem to be a significant threat. Will continue with a Flash Flood
Watch to cover this.
Precip will come to an end Sunday morning as the front exits the
state. Dry conditions will then round out the short term period.
LONG TERM...Sunday Night Through Friday
Drier air wl be overspreading the area as the aforementioned storm
system departs the region. Some wrap-around moisture wl traverse the
NW part of AR late Sun night and early Mon, producing some assocd
NWLY flow aloft is expected to prevail thru the middle of the week,
with dry conds expected thru Tue. Temps wl hover near or slightly
below normal lvls. A new storm system wl bring the next rain chance
to AR Wed thru Thu. Drier and cooler conditions wl return for late
Lake Wind Advisory from 10 AM Saturday to 9 PM CDT Sunday FOR
Flash Flood Watch through Sunday evening FOR Arkansas-Baxter-
Area Forecast Discussion
National Weather Service Spokane WA
445 PM PDT Fri Apr 28 2017
Scattered showers will bring brief periods of rain and possibly
graupel to north Idaho and northeast Washington this afternoon and
evening. The majority of Saturday should be dry before a frontal
system brings the potential for rain Saturday night and gusty
winds for Sunday. The middle of next week will be warm with
afternoon temperatures in the 60s to near 70 degrees.
Tonight: Scattered rain and graupel showers will produce brief
periods of precipitation this evening over the Idaho Panhandle and
northeast Washington. As of 230 PM, regional radar showed showers
under a 500mb cold pool (-27C to -28C) extending from Republic to
Davenport to Couer d`Alene to Sandpoint. RAP analysis suggests up
to 400 J/Kg of surface based CAPE over northeast Washington and
far north Idaho. There may be enough instability for a few
lightning strikes, but without a clearly defined shortwave kicker
to enhance lift, it is doubtful that any thunderstorms will become
very organized. By mid to late evening, upper level high pressure
will build over the Inland Northwest. The loss of surface heating
combined with warming aloft should cause most showers to
dissipate by 8 PM. It will be a chilly night with most areas
dropping into the 30s, under clearing skies and light winds.
Saturday: The majority of the Inland Northwest will be dry on
Saturday. The influx of moisture ahead of a frontal system will
bring increasing chances for showers to the northern Cascades in
the afternoon and evening, but the rest of our region will start
the day with some sunshine followed by increasing mid and high
clouds. Rain chances will likely peak after midnight Saturday. The
GFS, NAM and ECMWF are in good agreement that a cold front will
cross the Cascades overnight. The front will be accompanied by a
good deal of mid-level westerly flow which favors precipitation
over the Cascade Crest, the mountains of north Idaho and far
northeast Washington. The models suggest up to a quarter of an
inch in the Panhandle mountains with most of our region getting
less than a tenth. At this time, the Columbia Basin and Wenatchee
area look to get sprinkles at best.
Sunday and Monday: Sunday will be breezy behind Saturday night`s
cold front. Wenatchee to Mose Lake to Spokane and Pullman will
likely experience sustained west winds of 15 to 20 mph with gusts
to 30 mph for much of the day. Convective showers during the day
Sunday should be the most concentrated over the mountainous
terrain of the Idaho Panhandle and the Cascade Crest. Low chances
for showers have been included in places like Lewiston, Pullman,
Spokane, and Colville, but any showers in these lowland
communities should be brief. Monday will be less windy, but
chances for showers are in the forecast. The GFS, ECMWF, NAM, and
Canadian models depict a fast moving shortwave trough. Again,
mid-level westerlies should produce a rain shadow on Monday and
limit showers to the mountainous terrain of the Panhandle,
Northeast Washington, and the Cascade Crest. /GKoch
Monday Night through Friday: Northwest flow aloft is expected
Monday night as a weather disturbance moves across eastern WA and
north ID. Have increased our chance of precipitation during the
evening hours across the south central ID Panhandle. Kept a
mention of showers in the overnight hrs into Tuesday as the
disturbance exits. Tuesday night through Thursday will be be dry
as an upper level ridge builds into the area. 850 mb temperatures
warm to 15-16C late Thursday. Wednesday we will see temps 3-6
degrees above average, and Thursday 6-9 degrees above average.
Current forecast for Spokane next Thursday is 71. We haven`t seen
temps above 70 since last Sept 30th, when we were 75! Thursday
night onward there is very low confidence in the forecast. The
models all have differing solutions in how to break down the
ridge. Currently don`t doubt the breakdown of the ridge as this
spring`s weather patten has been progressive... However all models
have differing timing, strength and placement of a trough moving
into the Pac NW. Have kept mention of showers in for eastern WA
and north ID with a dry area across the Columbia Basin. Expect
this forecast to change as models hopefully come more in line with
the breakdown of the ridge. /Nisbet
00Z TAFS: Isolated showers and thunderstorms moving to the
southeast at around 15 mph are on the decline this evening
with most of the activity ending before 06Z Saturday. Weak
high pressure then moves in to allow the remainder of the
overnight and daytime hours Saturday to remain dry with VFR
conditions prevailing. /Pelatti
.PRELIMINARY POINT TEMPS/POPS...
Spokane 37 57 44 58 37 55 / 20 0 60 20 10 10
Coeur d`Alene 36 57 42 56 35 54 / 30 10 80 40 10 20
Pullman 38 59 45 58 37 55 / 20 0 70 40 10 10
Lewiston 41 65 49 64 42 60 / 10 0 40 40 10 10
Colville 36 58 42 60 37 56 / 20 10 30 20 0 30
Sandpoint 34 56 40 54 34 53 / 20 10 80 80 20 30
Kellogg 35 55 40 52 35 51 / 30 10 90 90 20 30
Moses Lake 37 63 47 66 40 63 / 0 0 10 10 0 10
Wenatchee 40 60 45 62 41 60 / 0 0 10 10 0 10
Omak 37 61 45 65 40 62 / 10 0 10 10 0 10
Area Forecast Discussion
National Weather Service Norman OK
1052 PM CDT Fri Apr 28 2017
Thunderstorms will form and move across southwestern and central
Oklahoma early Saturday. Some will likely produce very large hail
and damaging winds. Heavy rainfall will occur in a subsequent
large area of rain and thunderstorms from central Oklahoma
eastward along a slowly-moving front. Gusty north and northeast
winds will keep MVFR and IFR ceilings during the day Saturday.
.PREV DISCUSSION... /issued 723 PM CDT Fri Apr 28 2017/
Thunderstorms are expected to begin late this evening in
southern and western Oklahoma and move across central Oklahoma
during the early morning Saturday. Heavy rainfall will occuring
along a slowly-moving front Saturday morning. Gusty north and
northeast winds will bring MVFR and IFR ceilings during the day
PREV DISCUSSION... /issued 406 PM CDT Fri Apr 28 2017/
A warm layer and weak ridging aloft have helped prevent the
formation of thunderstorms, and this will likely continue to
inhibit storms until about 8 pm or so. Wide variations in severe
weather threats will cover our forecast area this evening, as
there will be large differences in vertical wind shear and CAPE,
along with several weak surface boundaries.
The short-range convective models show storms beginning to form
around 8 pm near a weak surface boundary roughly from Hobart to
Oklahoma City. These storms may become severe quickly, as they
will be in an area of strong shear and moderate CAPE.
Storms should gradually diminish (but still have substantial
severe weather potential) through the night, remaining mainly
near the original line of development. THere is also a
possibility of an MCS forming from convection in northwest
Oklahoma. In any case, strong to severe storms will be possible
across central and southwest Oklahoma through most of the night.
Heavy rain is expected with these storms, and training of cells is
likely, which could cause areas of rapid flooding. We extended our
previous Flood Watch west by three counties this morning, based on
the synoptic situation and the output of the models at the time.
There are indications from the HRRR and others that substantial
rainfall may occur a short distance west and north of our new
watch, but those areas generally have higher flash flood guidance.
This forecast issuance does not include any new changes to the
watch, but the evening shift will, of course, make any necessary
adjustments if model trends or convective trends suggest a
A very sharp cold front will move through the southeast half of
Oklahoma and into north Texas tomorrow. Most severe storms will
remain along and ahead of this front. The entire assembly should
exit our forecast area by midnight Saturday night. However,
instability under the upper low will continue a chance for showers
and perhaps a few thunderstorms into Sunday. The wraparound
precipitation area may include some snow mixed with the rain in
far northwest Oklahoma Sunday morning.
Monday will be a rain-free day, then another storm system will
arrive for midweek, bringing additional chances for showers and a
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 55 57 44 54 / 70 80 60 20
Hobart OK 48 50 40 54 / 70 70 50 20
Wichita Falls TX 58 61 44 62 / 40 70 50 10
Gage OK 43 45 35 46 / 90 70 60 50
Ponca City OK 50 53 44 51 / 90 80 70 50
Durant OK 70 80 50 63 / 40 80 70 20
OK...Flood Watch through Sunday morning for OKZ023>032-040>043-