Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/04/17
Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
700 PM CDT Tue Oct 3 2017
For the 00Z TAFs, a low confidence forecast with respect to all
elements. Amendments possible. Surface cold front will meander
around the region tonight and Wednesday morning before slowly
dissipating. Expect low cigs in the IFR and/or MVFR categories to
prevail through late Wednesday afternoon along with areas of fog.
In addition, occasional rain showers and a few thunderstorms are
expected to impact the terminal sites tonight and Wednesday.
.PREV DISCUSSION... /Issued 423 PM CDT Tue Oct 3 2017/
Cold front made a slow southward progression today before coming
to a halt near the Canadian River valley. Low- to mid-level
moisture remains plentiful even on the north side of the front,
with 850 mb dewpoints as analyzed by the RAP still remaining in
the 11 to 15 degree Celsius range behind the 850 mb front. Have
maintained healthy pops tonight as moist low-level upslope flow is
augmented by occasional disturbances in southwest flow aloft.
Frontal boundary expected to lift slowly north on Wednesday, with
warm advection and isentropic lift warranting continued high pops
through Wednesday night.
Chances for rain diminish a bit Thursday and more so Thursday
night as low-level winds become more southwesterly. Friday and
Friday night bring increasing chances for rain as final shortwave
trof passes, driving a cold front through the area.
Much drier post-frontal air brings dry weather back to the
Panhandles for the weekend. Next cold front Sunday night and
Monday brings a taste of autumn with high temperatures 10 to 15
degrees below climo and overnight lows falling well into the 40s
Area Forecast Discussion
National Weather Service La Crosse WI
530 PM CDT Tue Oct 3 2017
.SHORT TERM...(This afternoon through Wednesday)
Issued at 102 PM CDT Tue Oct 3 2017
Expecting more showers and storms to pop up going into late this
afternoon/evening as the cold front pushes into the area. Latest
CAMs (Convection Allowing Models) showing the cold front and
associated showers/storms pushing southeast out of the area by 10
pm or so. Have tailored pops to reflect this timing. Latest RAP
pushes MUCAPE this afternon into the 1000-1500J/kg range but this
may be a bit overdone given the amount of cloud over us inhibiting
full heating potential. 0-3km bulk shear in the 30-35kt range.
Will keep a close on on the potential for a few stronger storms
with small hail and gusty winds given the shear and cape if clouds
do develop holes which would allow more heating/instability.
Clearing expected then from the northwest to southeast after
midnight as the front clears the area and high pressure builds in
from the Northern Plains. Look for overnight lows in the middle
40s to the middle 50s.
A cooler/drier/mostly sunny day on tap for Wednesday as that area
of high pressure drifts overhead. Plan on seasonable temperatures
as highs top off in the 60s...with perhaps a few lower 70s across
far southwest WI/far northeast IA.
.LONG TERM...(Wednesday night through Monday)
Issued at 102 PM CDT Tue Oct 3 2017
An active/wet period setting up for Thursday through Saturday as a
couple areas of low pressure roll out of the Central Plains
into the Upper Mississippi River Valley region. The first area of
low pressure looks to impact the area Thursday into Thursday
night with incoming warm front and increasing moisture transport.
Instability/CAPE looks fairly limited with NAM indicating 0-3km
MUCAPE of 500-750J/kg. So, looks like mainly showers with embedded
thunder during this period. could be some pockets of heavier
rainfall as well with PWs pushing to around 1.5 inches south of
Frontal boundary looking like it will hang out across southern
WI/northern IL/northern IA Thursday night for continued shower and
storm chances mainly south of I-90. A stronger area of low
pressure ejects northeast out of the Central Plains and through
southern WI later Friday night into Saturday morning for another
round of shower/storms and possibly pockets of heavier rainfall as
PW values push up into the 1.5-1.8 inch range mainly across the
south and east.
Mean areal average rainfall from Thursday through Saturday looks
to range from 1/4 to 1.5 inches, with pockets of heavier amounts.
This should put a dent in the abnormally dry/drought conditions in
place across our area.
Sunday looks mainly dry as another cold front swings through but
then rain chances return Sunday night into Monday from central WI
into northeast IA as southwest flow aloft brings another wave of
low pressure through IL.
Otherwise, temperatures are expected to remain right around
.AVIATION...(For the 00Z TAFS through Wednesday evening)
Issued at 530 PM CDT Tue Oct 3 2017
Cigs/WX/VSBY: cold front sweeping through the region early this
evening - already passed KRST and should do so at KLSE before 00z.
Scattered -shra/ts along and post the front. Brief ifr/MVFR vsby
reduction possible with any of the heavier rainfall. Some MVFR cigs
also post the front for 1-3 hours. By mid evening the skies clear
under the influence of high pressure, and should hold that way
through Wed evening.
Wind: generally light west/northwest, picking up bit by Wed
afternoon but holding from that direction.
Area Forecast Discussion
National Weather Service Billings MT
711 PM MDT Tue Oct 3 2017
Water vapor imagery shows our region being under a col between a
departing low in ND and a cutting off low over the Great Basin.
Shower activity has ended as surface high pressure has settled in,
and main forecast concerns are cold temps and fog potential. There
is an area of upslope cloud along the eastern slopes of our
western mountains, and this could have an impact on both temps and
fog, but indications are that this will erode over time. Most if
not all of our cwa will see temps fall below freezing tonight.
Records at Billings (27), Miles City (27) and Sheridan (25) will
be challenged, again depending on cloud cover. Weakening winds and
clearing skies, along with dew points in the mid 20s to lower
30s, point toward the potential for fog. Have expanded patchy fog
coverage a bit (including at Billings), but latest HRRR runs have
actually trended toward less overall coverage. Would be surprised
if there wasn`t some localized fog in river valleys by sunrise.
.SHORT TERM...valid for Wed and Thu...
Upper low over NW North Dakota is slowly shifting northeastward
and filling. Its influence is decreasing as isentropic lift and
upper divergence shift with it. High resolution models have
handled precipitation the best so far today, and following their
lead will keep a slight chance of rain/snow showers over Fallon
and nearby areas through the early evening. We should otherwise
see decreasing clouds tonight. Our main weather message for
tonight is a first "hard freeze" for many locations at the lower
elevations (28 degrees or lower for a few hours). We do not issue
highlights for this, but will message through social media and our
For Wednesday, after a chilly start we should see some warming
over todays readings. However, another cut off upper low over
Nevada will slowly lift northward and bring our western mountain
zones under a divergent flow with increasing mid level moisture.
SO some rain or snow showers are possible by late afternoon. Some
of the lift and moisture moves across the plains as well tomorrow
night. The air associated with this system is from the south so we
do not anticipate much if any snow overnight, but perhaps a mix
after midnight. Main precipitation band lifts north of us by
Thursday morning but proximity of upper low over our CWA may lead
to rain and snow showers in the mountains and nearby areas through
Thursday night. Any accumulations should be of on the meager side
and of little impact. BT
.LONG TERM...valid for Fri...Sat...Sun...Mon...Tue...
Models are overall in good agreement through the upcoming
weekend. An upper low and trough will move east into the central
high plains with brief ridging building across our forecast area
Friday. This will be short-lived as a strong upper low and trough
drop southeast out of Canada Friday night into Saturday. This will
also bring a strong cold front across the forecast area during
the day Saturday. Pressure gradients will be tight ahead of the
front resulting in gusty southwest winds especially for the Big
Timber to Livingston areas. Very little if any precipitation is
expected along the front. However, by Sunday shower chances return
as the upper low and trough will be situated over the state.
Temperatures will be normal Friday and Saturday with readings in
the lower to middle 60s. Readings will be much cooler Sunday with
50s likely, and especially Monday and Tuesday when highs in the
40s will be possible. Hooley
Skies will gradually clear from west to east during the late
evening and overnight hours with mostly clear skies expected after
06z. Expect the gusty northwest winds to subside shortly after
sunset. Some patchy fog and reduced visibilities are possible for
areas along and north of a KLVM-KBIL-4BQ line after 06z through
12z Wednesday. Otherwise, expect VFR conditions into Wednesday.
.PRELIMINARY POINT TEMP/POPS...
Wed Thu Fri Sat Sun Mon Tue
BIL 027/054 035/057 038/065 045/064 040/053 034/047 031/046
00/U 31/B 11/U 01/B 23/W 21/B 11/B
LVM 025/050 032/053 035/062 043/062 036/048 030/045 025/043
02/W 32/W 21/B 01/N 24/W 31/B 11/B
HDN 025/059 035/058 038/066 042/066 039/055 035/049 031/048
00/U 21/U 11/U 01/B 23/W 21/B 10/B
MLS 027/056 037/057 038/063 043/065 039/055 034/047 030/045
00/U 31/B 01/U 01/N 11/B 11/B 10/B
4BQ 026/058 038/057 038/062 042/066 039/053 034/047 031/044
00/U 21/B 11/B 01/U 22/W 11/B 10/B
BHK 026/056 038/056 037/061 042/064 038/053 034/046 030/042
10/U 21/B 01/B 01/N 11/B 01/B 00/B
SHR 025/058 035/057 035/062 038/067 037/052 032/047 029/044
01/U 11/U 11/B 00/U 33/W 31/B 10/B
Area Forecast Discussion
National Weather Service Houston/Galveston TX
933 PM CDT Tue Oct 3 2017
At 01z, sfc high pressure was located over eastern MS and another
surface high was over SW KS. There is still a strong onshore flow
and showers continue to develop over the western Gulf and move
inland. 00z soundings show PW values between 2.20 and 2.45 inches
so the air mass still looks plenty moist. Drier air is progged to
move southwest late tonight and moisture levels will begin to
drop. At 300 mb, upper level ridging is becoming centered over
south Texas. At 850 mb, high pressure was noted over NC and this
feature was inching westward. 850 moisture still looks robust with
850 dew points around 16 C. Will maintain the 30-40 PoPs currently
in the grids but did raise min temps a degree or two in places as
confidence is low that the drier air well off to the east will
make it here by morning. Wet ground may lead to some light fog by
morning but left that out of the grids at this time due to mixing
from winds and extensive cloud cover. 43
City of Houston established a new annual rainfall record with
74.18 inches of rain so far in 2017. It`s hard to believe that an
annual record was broken with almost a full 3 months to go in the
year, but it is what it is. The previous record rainfall for a
year was 72.86 inches set back in 1900. 43
.PREV DISCUSSION... /ISSUED 639 PM CDT Tue Oct 3 2017/
Some patchy areas of IFR/MVFR will affect KIAH and the nearby
aviation sites through 02/03Z. Otherwise, isolated to scattered
showers will linger through at least mid evening. There is a
general downward trend in the models regarding rain chances;
although, for KIAH, KHOU, and KSGR the NAM12 has another better
chance of rain between about 08Z and 11Z. If the cloud cover
clears out enough later this evening or overnight tonight could
see at least patchy fog to form. The more likely scenario is for
a mid or high level VFR deck to persist overhead which will keep
fog formation chances low. The models and guidance both suggest an
MVFR deck will be possible late tonight into early morning
Wednesday. Any low decks or fog that do form should lift to VFR by
PREV DISCUSSION... /ISSUED 344 PM CDT Tue Oct 3 2017/
Scattered showers and thunderstorms seen on radar imagery this
afternoon, expected to hang around through much of the early evening
hours. Locally heavy rainfall and higher rain rates will be possible
in isolated stronger storms. Should see coverage begin to shift into
the western portions of our forecast area closer to sunset. GOES-16
precipitable water imagery still shows the best moisture over the
western half of SE TX and further west of the forecast area. Short
term guidance such as the HRRR and RAP13 continue widely scattered
to isolated precip mainly over the western reaches into the early
Should continue to see partly to mostly cloudy skies overhead
through late Wednesday and into early Thursday, until upper level
ridging begins to build in over the region. This area of high
pressure will slide westward by late Friday, which should allow
for more of a summer like pattern to return to the forecast
Saturday. Saturday through Monday kept PoPs (20%) mainly
concentrated along the coast, associated with the typical daytime
heating and sea breeze pattern. Temperatures through the remainder
of the week should remain 4 to 7 degrees above normal for this
time of year.
Early next week, global models are still indicating a frontal
passage pushing through the region. Based on the most recent runs of
the GFS and ECMWF, there is still lack in agreement on timing of the
front, as well as the amount of precip expected out ahead of the
boundary. GFS and the Canadian model solutions are a tad slower than
the ECMWF. GFS places more rainfall out ahead of the frontal
boundary itself, moving into SE TX late Tuesday into early
Wednesday. On the other hand, the ECMWF brings less precip out ahead
of the front into the region Monday afternoon into early Tuesday.
Currently trending the forecast more towards the GFS and Canadian
solutions, in terms of both timing and PoPs. With this system a
week out, there is still plenty of time for the models to get a
better handle on both strength and timing. Regardless, should see
cooler temperatures behind the front along with drier conditions.
We will continue to monitor an area of low pressure currently
located in the southwestern Carribean Sea near Panama, expected
to move towards the NW Caribbean. The National Hurricane Center
have increase the formation chance up to 40% over the next 48
hours and 60% over the next five days, of the system becoming a
The pressure gradient will remain tight across the northern Gulf
of Mexico tonight through much of Wednesday with higher pressures
along the northern Gulf. This will maintain a long fetch of
moderate to strong easterly winds. Seas should build to near 9
feet in offshore waters Wednesday into Wednesday night. These
building seas have started piling water up along the upper Texas
coast. Current water levels are running about 1.5 to 2 feet above
normal tide table values. These levels will be capable of
producing minor coastal flooding around times of high tide along
the more susceptible roads along the Bolivar Peninsula, Blue Water
Highway and Beach Drive in Surfside. As confirmed by Galveston
Beach Patrol this morning, rip currents will also be a high risk.
The Beach Hazards Statement in place discusses the high tides,
elevated surf and rip currents. The statement will remain in
effect through at least Wednesday, possibly into Thursday. Winds
and seas will gradually decrease Thursday into Friday with low
winds and seas for the weekend.
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 74 87 69 88 67 / 50 10 0 10 10
Houston (IAH) 74 87 70 88 68 / 50 10 10 10 10
Galveston (GLS) 80 87 78 88 77 / 50 30 30 10 10
GM...SMALL CRAFT SHOULD EXERCISE CAUTION through Wednesday evening
for the following zones: Galveston Bay...Matagorda Bay.
Small Craft Advisory until 7 PM CDT Wednesday for the following
zones: Coastal waters from Freeport to the Matagorda Ship
Channel out 20 NM...Coastal waters from High Island to
Freeport out 20 NM...Waters from Freeport to the Matagorda
Ship Channel from 20 to 60 NM...Waters from High Island to
Freeport from 20 to 60 NM.
Area Forecast Discussion
National Weather Service Indianapolis IN
1136 PM EDT Tue Oct 3 2017
Aviation section updated
Issued at 337 PM EDT Tue Oct 3 2017
The forecast period will be much more active than the last
few weeks as a series of low pressure systems passes through the
forecast area over the next seven days. The first is progged to
start affecting central Indiana this evening with its associated
cold front eventually stalling over the Lower Midwest through the
end of the week. At that point, the second low pressure system will
finally push that front farther north early in the weekend, but
showers and thunderstorms will remain in the forecast through
Saturday as the second low moves through. After brief ridging and
dry conditions on Saturday night and Sunday morning, yet another
system will pass through Ontario. Its associated cold front will
bring additional chances for showers and isolated thunderstorms late
in the extended period.
.NEAR TERM /Overnight/...
Issued at 951 PM EDT Tue Oct 3 2017
Surface analysis late this evening shows strong high pressure over
the east coast. A weak cold front was found across Wisconsin and
Iowa. Water vapor imagery shows a stream of moisture stretching
from Texas across Illinois to the Great Lakes...edging into NW
Cold cold front and associated moisture stream are expected to sag
southeast across Indiana overnight. As this stream of moisture
arrives...cloud cover should increase along with chances for
rain. HRRR shows possible -shra development overnight. Time height
sections show good saturation within the lower and mid
levels...but minimal forcing. The 310K GFS Isentropic surface show
weak upglide amid a moist surface. Thus keeping some pops in
place overnight appears reasonable given the good moisture but
weak forcing...However any amounts that may occur will be quite
Given the expected clouds and ongoing weak warm air
advection...will trend lows at or above forecast builder blend.
.SHORT TERM /Tomorrow through Friday/...
Issued at 337 PM EDT Tue Oct 3 2017
Showers and thunderstorms will remain in the forecast through
tomorrow across most of the forecast area as a cold front
continues its passage. Confidence remains medium to high in best
chances being over the northwestern third of the forecast area
through the morning hours. After that, forcing will begin to wane
a bit as the front moves farther south, but upper forcing will
keep chance pops (north) and slight chance pops (central) in the
forecast until that front shifts back north and stalls over the
area on Thursday. Again, highest chances for showers and
thunderstorms will be across the northern half of the forecast
area along the frontal boundary through the end of the forecast
period. Meanwhile, temperatures through the period will remain
above normal with highs ranging from the mid 70s to low 80s and
overnight lows in the 60s, stuck with latest model blend
.LONG TERM /Friday night through Tuesday/...
Issued at 256 PM EDT Tue Oct 3 2017
A seemingly wet extended timeframe with numerous chances for
precipitation. The period begins friday night with an approaching
upper wave and associated low and cold front from the central
plains. Mid/long-range models are in decent agreement as to the
timing of the impacts into the area. Thunder remains a possibility
with the showers along and ahead of the front pushing into the
area Saturday afternoon/evening. Model solutions then begin to
diverge and confidence begins to wane in how the next upper trough
will eject/evolve from the upper plains. ECMWF is more progressive
and more amplified with its solution than the GFS...leading to
earlier and more precipitation early next week. Stuck close to
model initialization blend...as confidence not high in which
solution may be the correct one. Above normal temps look to
continue into the extended timeframe...except toward the end when
a return to normal arrives by Tuesday...maybe later if the GFS is
.AVIATION /Discussion for the 040600Z IND Taf update/...
Issued at 1136 PM EDT Tue Oct 3 2017
VFR Conditions are expected this TAF Period.
Water Vapor continues to shows a stream of moisture from TX to
Illinois and Wisconsin...with some cloud streaming east into west
Central Indiana. This stream of moisture is expected to push
slowly east and become more east-west oriented as a weak cool
front sags out of the upper midwest. Any CIGS as these feature
approach should be VFR.
Models continue to suggest a lack of organized forcing and only a
stray shower or storm will be expected. Confidence too low to
provide specific timing for this event. Thus used a VCSH window
for when best moisture appears present.
Best window for TSRA looks like during daytime heating hours on
Wednesday afternoon...however forecast soundings appear to show
limited instability. Thus confidence for any thunderstorms is low.
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
1002 PM EDT Tue Oct 3 2017
High pressure will dominate the weather through most of this
week. Low pressure and unsettled weather regime is possible for
late this weekend into early next week.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As of 955 PM Tuesday...A clear sky over most of the forecast
area has allowed temps to cool back into the 60s most spots.
Min temps from low to mid 50s inland to low- mid 60s coast still
look on track. An area of clouds off the coast are just now
moving onto the Outer Banks. We are seeing a few sprinkles with
these just offshore of Cape Hatteras. Returns farther south and
west north and northeast of New Bern are associated with a clear
sky and likely are chaff. Will continue a slow increase in
clouds along the immediate coastline with a slight chance of a
light shower here. Best chances will be across the Outer Banks
but even here the increase clouds is expected to be more
pronounced than any rain shower threat.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
As of 300 PM Tuesday...Subtle wind shift to E-SE around 900 MB
will continue, allowing additional influx of offshore moisture
resulting in increased SCU and scattered shower threat along
coast with slight chance POPs inland to Hwy 17. Max temps mid to
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
As of 4 PM Tue...High pressure will remain the dominant feature
over region through the first half of the weekend continuing
the period of mainly dry weather. The high will shift offshore
late weekend into early next week with some unsettled weather
and a return to warm and humid conditions.
Wednesday night through Saturday...With the high still ridging
into E NC from offshore and light NE to E winds, conditions
will be near climo with mild days and cool nights. Have fcsted
overnight lows with cooler MET/ECS MOS vals due to good
radiational cooling and low TD`s. There will be some patchy fog
each early morning as T-TD spreads will be near 0 each
night/morning. Highs will steadily warm each day as low lvl
thicknesses rise into the 1420M range by Sat, with readings in
the mid 80s interior to low 80s beaches. Overnight lows will
start out cool initially with mid 50s interior to low 60s
coast, then moderate to low 60s inland to mid/upr 60s coast by
Sunday through Tuesday...There is still model dispute on
evolution of shortwave energy and potential tropical development
that will lift NE out of the GOM late in the weekend into early
next week. 03/12Z CMC/GFS indicate a slower and more westward
propagation of this activity across the TN valley, while latest
ECMWF is more in line with its previous 03/00Z ensemble mean,
which is quite unsettled across E NC with tracking shortwave and
tropical disturbance through the Carolinas from the Gulf coast.
Have therefore continued just chc pops, highest inland, for the
Sunday/Monday period. Will have to continue watching trends as a
heavy rain/flooding threat may develop if ECMWF advertised 2+
inch PWATS verify for Sunday and Monday. A return to to warm
and humid summery-type regime with highs well into the 80s and
muggy overnight lows between 70-75 late weekend through early
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Short Term /through 18Z Wednesday/...
As of 755 PM Tuesday...VFR will through 06Z. Late tonight there
is better potential for fog and low clouds producing sub VFR
conditions after midnight as the low level flow becomes easterly
and moistens a shallow near ground layer. Latest RUC continues
to indicate period of IFR to LIFR likely 08Z- 12Z for most
sites with lowest VSBYs and longest duration at KPGV and KISO.
Soundings look a little less certain for KEWN and based on past
observations, only show 3SM and MVFR here. Conditions improving
to VFR quickly after 14Z Wednesday with scattered SCU
developing rest of morning.
Long Term /Wednesday night through Sunday/...
As of 4 PM Tue...Pred VFR conditions expected through the
period, though could see early morning sub-VFR fog and stratus
develop each late night and early morning through the period.
Short Term /through Wednesday/...
As of 955 PM Tuesday...Northeast winds continue mainly 15 to 20
kt with a few gusts into the lower 20s. With seas still running
5 feet to around 6 outer waters, continued SCA through tomorrow
for marginal conditions on the waters. Pressure gradient over
the waters will weaken later tonight and Wednesday, allowing
winds to diminish to 10-15 KT and seas to subside below 6 ft by
Long Term /Wednesday night through Sunday/...
As of 4 PM Tue...Strong high pressure will gradually slide
offshore mid to late week. Generally easterly flow 5-10 kt
expected through Friday. Winds veer SE for Sat and Sun though
remain generally in the 5-10 kt range, with some higher 15 kt
gusts for the coastal waters. Seas will be 2-4 ft northern
waters to 3-5 ft southern and central waters through the period.
NC...Beach Hazards Statement from 8 AM EDT Wednesday through
Wednesday evening for NCZ095-103-104.
MARINE...Small Craft Advisory until 8 PM EDT Wednesday for AMZ152-154-
Area Forecast Discussion
National Weather Service Paducah KY
442 PM CDT Tue Oct 3 2017
Issued at 439 PM CDT Tue Oct 3 2017
Updated Aviation discussion for 00Z TAF Issuance.
.SHORT TERM...(Tonight through Thursday night)
Issued at 305 PM CDT Tue Oct 3 2017
Main issue in the near term remains the potential for widely
scattered showers and isolated thunderstorms through midday
Wednesday, especially across portions of southeast Missouri and
An upper level ridge situated from the eastern Great Lakes to the
Tennessee Valley and Gulf of Mexico will be suppressed into the
Southern Plains by Thursday. Meanwhile, surface high pressure will
remain anchored off the Atlantic Coast. Southerly flow on the back
side of this high will maintain warmer than normal temperatures
through the period.
Widely scattered showers impacted portions of southeast Missouri
and southern Illinois today. Expect the potential for another
round or two of widely scattered showers and isolated thunderstorms
tonight into midday Wednesday as weak energy ripples through the
moist southwesterly flow on the west side of the upper level high.
Much of the period from Wednesday afternoon through Thursday night
should remain dry as the active weather focuses across the Plains
into the Upper Midwest along a frontal zone. Some models suggest
the potential for showers may infringe upon our northern tier of
counties in southern Illinois and southwest Indiana late Thursday
night, so we maintained a slight chance there.
Temperatures through the period will largely be influenced by the
amount of sky cover, with highs averaging in the lower 80s and
lows in the lower 60s. Areas that hang on to more cloud cover may
experience highs in the upper 70s and lows in the mid 60s, while
locations with more clearing see highs in the mid 80s and lows in
the upper 50s.
.LONG TERM...(Friday through Tuesday)
Issued at 305 PM CDT Tue Oct 3 2017
Forecast confidence is fairly high through Saturday and then
decreases Sunday through Tuesday.
There has been reasonable agreement in the GFS and ECMWF for the
last few cycles of the remaining portion of the current western U.S.
trough pivoting out of the central and northern Plains into the
Upper Midwest Friday through Saturday. This will bring a decaying
cold front eastward into our region Saturday.
The models have been consistently indicating that the associated
frontal band of convection will dissipate as it attempts to move
through our region. Decent chance PoPs are warranted over southeast
Missouri, southern Illinois and southwest Indiana, with only small
chances over much of west Kentucky. The front will be losing its
focus over our region and will not pack much of a punch as far as
temperatures are concerned either. Clouds will hold temperatures
down a few degrees from Friday, but it will still be well above
We will remain in southwest flow aloft behind this initial system,
and the primary surface boundary will re-establish itself to our
northwest. Current indications are that most of the area will be dry
and continued warm on Sunday.
One fly in the ointment for late Sunday into Monday is the potential
for a tropical system, as yet not developed, to lift northward into
the Tennessee Valley, potential spreading some rainfall into west
Kentucky. The GFS and ECMWF each have a system of some strength, but
the ECMWF is a bit farther east and slower than the GFS. We will
have to keep a wary eye to the south through the end of the week, as
it seems most landfalling tropical systems like to visit the
MS/OH/TN valley region.
Heading into Monday and Tuesday, the 12Z GFS initially has an
elongated upper trough from the northern Rockies east northeast into
northern Ontario. The troughing will solidify into a closed low near
International Falls by 00Z Wednesday. The associated cold front
moves through our region Tuesday with a decent chance of convection,
but it should be fairly dry Monday and Monday night. The heat would
continue across the region Monday and then the cool/near normal air
would start to move in Tuesday. Unfortunately, the 00Z ECMWF is much
more amplified with the upper trough, and pushes it and the cold
front through our region Monday and Monday night.
The result of the models` lack of agreement is a steady dose of
chance PoPs for all or a portion of the area from Sunday through
Tuesday. Instability when it develops will be meager, so any
thunderstorms will be on the weaker side, with a very localized
heavy downpour and sporadic lightning the primary concerns.
Issued at 439 PM CDT Tue Oct 3 2017
Rap, Nam, and Hrrr short res modeling keeps pcpn west of terminals
after 00Z. Will monitor for vicinity mention necessity, however,
early in period. Otherwise time/height cross sections suggest we
lose the lower VFR deck and go scattered to broken mid and high
decks overnight. The lower VFR bases will reappear with diurnal
fueling tmrw, with the best chance for ceilings during the late
pm hours at KEVV and KOWB.
...Update to aviation forecast discussion...
.SHORT TERM...(This evening through Wednesday)
Issued at 250 PM CDT Tue Oct 3 2017
WV satellite imagery and 12Z observed obs suggest upper level
forcing and jet energy remain largely north of the forecast area
into the Upper Plains region. Lower level front is draped from
southeastern NE into northeastern KS back into central KS. Weak
convergence is finally leading to moderate to heavy drizzle over
portions of the area mainly from Falls City, NE back to the
northwest of Manhattan, KS. This is all associated with the low
level frontal lift through about the 925mb level.
Expectation this afternoon is for drizzle to slowly develop into
showers generally north of I-70 and along the Hwy 15 corridor. VIS
imagery suggests some clearing has taken place generally southeast
of Topeka, KS. So, destabilization with plentiful moisture in place
could allow for a few showers to develop into thunderstorms with
around 25-30kts of effective shear in place. Lightning will likely
be the main hazard. Forecast confidence has been low with overall
set up but some short-term guidance does seem to be catching on with
the HRRR suggesting afternoon and early evening storms developing
with post-frontal showers developing overnight into the early
morning behind the surface boundary. ARW and NMM models also have
generally come into similar agreement. Weak and broad isentropic
lift therefore is the likely factor into the morning. Could keep
showers going long enough to drop anywhere from .25-.75 inches of
precipitation over portions of the forecast area. Expecting some
possible reduced cloud cover and visibility with patchy post frontal
fog developing as well generally after the 5Z time frame.
Temp gradient remains in place from northwest to southeast over the
area this afternoon and evening following with the frontal
progression. Highs this afternoon top int the mid 60s northwestern
portion of the area and low 80s over the southeastern portions of
the area. Lows will bottom in the mid 50s to mid 60s again from
northwest to southeast.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 250 PM CDT Tue Oct 3 2017
On Wednesday night a mid level shortwave will lift out over the
northern plains, which will cause the surface warm front to lift
northward. Within the warm sector deep isentropic lift is expected
to increase overnight and continue through Thursday evening. Each
model is depicting several rounds rainfall during this time frame.
There is no obvious focus for additional lift, but with southwest
flow aloft a subtle shortwave could not be ruled out. There will
also making it difficult to pin down the exact timing and locations
of the rainfall. Model soundings are indicating that pwats approach
2 inches and warm cloud depths around 13 kft therefore heavy
rainfall rates will be possible. On Friday the main trough exits the
Rockies and pushes a cold front through the area. Large scale lift
associated with this trough coupled with frontogenesis along the
frontal zone and ample moisture should set the stage for one last
round of rainfall. The deep layer shear will become parallel to the
front, which supports the possibility for more heavy rainfall. One
main question is the amount of instability will exist in the warm
sector given the chances for cloud cover and precipitation prior to
the front arrival. Quick to follow will be a deeper longwave trough
to drop out of western Canada. A much stronger surface high builds
into the region brining more seasonable temperatures.
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 632 PM CDT Tue Oct 3 2017
Main question is duration and timing of limiting ceilings and
confidence in any particular category persisting is low. Cold
front just passed TOP and will move through FOE shortly.
Primarily MVFR cigs follow though some variation in obs noted.
Most guidance seems too high for the most part and have stayed
with MVFR prevailing, to IFR after 09Z as boundary layer
saturates and front stalls over southern KS. Will suggest some
improvements after 15Z. Kept VCSH with limitations in any showers
Area Forecast Discussion
National Weather Service Tucson AZ
350 PM MST Tue Oct 3 2017
.SYNOPSIS...Expect isolated to scattered showers and thunderstorms
east of Tucson late tonight into Thursday evening. Dry conditions
will then prevail Friday into next Tuesday. Unseasonably warm
daytime temperatures will prevail into this weekend, then high
temperatures will cool closer to seasonal normals by the middle of
.DISCUSSION...A broad positively tilted upper trough continues over
the western CONUS this afternoon, low pressure centered over
northern California. Meanwhile, a highly amplified upper ridge was
over the eastern CONUS. Moisture is expected to increase especially
across eastern sections of this forecast area by daybreak Wednesday.
The 03/12Z Univ of AZ WRF-NAM and WRF-GFS and to some extent the
03/21Z HRRR were similar with depicting a few showers to occur
across the White Mountains late tonight or toward sunrise Wednesday.
Expect dry conditions area-wide this evening followed by isolated
showers and thunderstorms across the White Mountains late tonight.
The 03/12Z NAM/GFS/ECMWF/CMC remained consistent versus their
respective previous solutions with depicting high pressure aloft to
expand westward over the southern CONUS Plains Wednesday. Meanwhile,
generally southwesterly flow aloft across this forecast area
continues Wednesday as the northern California low is ejected into
southern Idaho. Enough moisture is progged by the various solutions
to support isolated to scattered showers and thunderstorms east of
Tucson Wednesday into Thursday. The favored periods for any showers/
tstms to occur are the afternoon/evening hours. A slight chance of
showers/tstms continues mainly near the New Mexico state line
Deeper moisture is progged to be shunted well east southeast Arizona
Friday as a broad upper ridge becomes positioned well south of the
area, and a ridge axis amplifies along the West Coast. The inherited
PoPs were reduced to just single digits Friday based on these
solutions. Thus, precip-free conditions area-wide Friday followed by
clear skies this weekend and likely through at least Monday.
Thereafter, the 03/12Z GFS depicted a strong tropical system to
approach the southwest Baja California coast around the middle of
next week. Only one other GFS ensemble member depicted this system,
and a quick glance at the 03/18Z GFS was similar to the ECMWF and
other GFS ensembles with not having this system near that area.
Thus, continued dry conditions next Tuesday under clear skies or
mostly clear skies.
Expect unseasonably warm daytime temperatures into this weekend
followed by daytime temperatures lowering closer to seasonal normals
around next Tuesday.
.AVIATION...Valid thru 05/00Z.
Isolated -TSRA/-SHRA may occur across the White Mountains northeast
of KSAD late tonight. Expect isolated to scattered -TSRA/-SHRA
Wednesday generally east of a KSAD-KFHU line. Otherwise, clear skies
or a few clouds above 20k ft AGL west of KTUS. KTUS vicinity
eastward to the New Mexico state line, few to scattered clouds
around 8k-12k ft AGL tonight, then few to broke clouds around 6k-10k
ft AGL Wednesday. Gusty ely/sely surface wind to 20 kts at times
east of KTUS. Surface wind variable in direction mainly less than 12
kts elsewhere through the period. Aviation discussion not updated
for TAF amendments.
.FIRE WEATHER...A few showers and thunderstorms may occur late
tonight across the White Mountains, then isolated to scattered
showers and thunderstorms are expected east of Tucson Wednesday into
Thursday. A slight chance of showers and thunderstorms exists across
the White Mountains Thursday night, then dry conditions return area-
wide Friday into next Tuesday. 20-foot winds will generally be
terrain driven less than 15 mph into early next week. However,
occasional afternoon gusts to 25 mph will occur.
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