Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/16/18
Area Forecast Discussion
National Weather Service Bismarck ND
1021 PM CDT Wed Aug 15 2018
.UPDATE...
Issued at 959 PM CDT Wed Aug 15 2018
Little change with this update. The main challenge for tonight will
be determining potential smoke impacts, especially to surface
visibility on Thursday. It may be the case where smoke is quite
thick aloft, while weak low level flow trajectories remain
unfavorable to advect significant near surface smoke into western
and central North Dakota. However, this is somewhat uncertain.
UPDATE Issued at 640 PM CDT Wed Aug 15 2018
Did trend towards the lower edge of forecast guidance for low
temperatures tonight given the dry airmass in place despite the
weak return flow that is forecast. Widespread low temperatures in
the lower 50s are forecast, closer to the bias corrected
statistical guidance. Also added a mention of smoke to much of the
west and the north for Thursday as the thick shield of smoke
across north central Montana into Saskatchewan and Alberta may
continue to propagate east-southeast downstream of the upper level
ridge axis. This is depicted in the experimental HRRR and RAP
smoke guidance.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 303 PM CDT Wed Aug 15 2018
Water vapor imagery shows an upper-level low spinning over western
SD this afternoon. Shower and thunderstorm activity associated with
this low has stayed well off to our south, with surface high
pressure and sunny skies entrenched over ND. With the high sliding
off to the east tonight and warmer temperatures this afternoon,
tonight should not be as cool as the previous two.
The upper low will slowly drift eastward into Thursday as the next
upper-level ridge begins to build over MT/WY. Gradual height rises
will allow for slightly warmer temperatures on Thursday, with highs
in the mid 80s to lower 90s.
GOES-16 visible imagery shows widespread smoke over southern
Alberta into southwest Saskatchewan. Some of this smoke may be
transported into northern ND on Thursday, which is supported by
the 12Z HRRR/RAP Smoke Models. Confidence is not high enough to
add a smoke mention to the forecast at this time, but will
continue to monitor.
.LONG TERM...(Thursday night through Wednesday)
Issued at 303 PM CDT Wed Aug 15 2018
The upper-level ridge will slide over the Northern Plains Thursday
night into Friday. Some of the guidance is hinting at a weak
disturbance moving through on Friday, but it`s tough to find low-
level forcing/moisture to support any precipitation.
A shortwave trough is forecast to move onto the Pacific Northwest
coast on Friday, reaching the Northern Plains by Saturday evening
while interacting with a northern stream trough and attendant
surface cold front. This will give our area the best chance for
widespread precipitation we have seen in quite some time, mostly
from Saturday evening into Sunday afternoon. More than enough
instability (around 2000 J/kg) will be in place for thunderstorms
Saturday evening, and a few storms may become strong (Note: GFS
surface dewpoints have consistently been too low - on the order of
10F - and therefore, its instability analysis is an outlier and
should be ignored). Shear looks very limited though, so severe
weather is not anticipated at this time.
As for temperatures, trended toward the warmer side of
guidance for both Friday and Saturday highs. With the cold front
just making its way into western ND Saturday afternoon, think
Saturday may actually be the warmest day for central parts of the
state. However, Sunday will be much cooler as Canadian air begins to
filter in behind the front. In addition, cloud cover may help in
keeping temperatures down on Sunday.
Cooler weather looks to continue through early next week as we
remain under northwest flow aloft. Both the GFS and ECMWF resolve a
disturbance or two passing through the region Monday through
Wednesday, but there are timing and amplitude differences.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 959 PM CDT Wed Aug 15 2018
Smoke may increase across western and central North Dakota on
Thursday, and introduced a smoke mention to the KISN/KDIK/KMOT
TAFs for now. There is some uncertainty on how far south the smoke
will reach and how low visibility may become.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...PA
SHORT TERM...Hollan
LONG TERM...Hollan
AVIATION...PA
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
733 PM EDT Wed Aug 15 2018
.AVIATION...
Arc of isolated showers lifting northward through Detroit terminals
is along the 800-700mb warm front extension and deeper moisture
axis. Showers will lift into an area of stronger midlevel subsidence
and high static stability between 6.0 and 9.0 kft agl. Expectations
are for this shower activity to dissipate this evening. Southeast
Michigan will then see placement within a greater warm conveyor that
will be east of a midlevel low pressure system lifting toward the
state. Secondary moisture advection and strong convergence
associated to low pressure system will impact the area for much of
Thursday. Will likely see an increase in shower and thunderstorm
activity after 10Z Thursday morning and persist in an isolated to
scattered coverage through the early to middle afternoon. For now
will just include shower mention and leave thunderstorms out of the
forecast. Moderate potential will exist for some periods of IFR cig
heights at the Detroit terminals between 10-18Z.
For DTW...Best chance of heavy rain looks to be around 14-18Z though
models have been shifting this window around. Thunderstorms are
possible but not high enough confidence to include in the taf.
.DTW THRESHOLD PROBABILITIES...
* Low for thunderstorm through Thursday.
* Medium for cigs aob 5000 feet 06-12z, high after 12z.
&&
.PREV DISCUSSION...
Issued at 346 PM EDT Wed Aug 15 2018
DISCUSSION...
Upper-level ridging and dry conditions in the low to mid-levels (as
noted by low RH 65% and mid RH 30% in the 12Z DTX sounding) have
allowed dry conditions to persist throughout the morning and
afternoon. High cirrus will continue to fill in throughout the
evening, ahead of an approaching shortwave trough, with overcast low-
level stratus filling in overnight as the low and mid-levels
saturate.
Attention will then turn to rain and thunderstorm chances which are
expected to take place throughout Thursday as a shortwave trough and
adjoining surface low pressure system pushes northeast across the
CWA. Increased southwest gradient flow will usher in subtropical
moisture into the region as noted by the latest 12Z GFS20 run, where
PW values range between 1.80 - 2.00 inches between Thu 06 - 12Z.
Latest NAM12 and RAP model suites also support PW values in this
range, which would be near-record to record values according to the
SPC sounding climatology page for DTX. Latest 12Z suites show axis
of greatest moisture transport and leading edge of the LLJ to push
into Ohio and perhaps the southern Metro region of Michigan between
06-12Z, which will be an area to focus on for initial heavy showers
and thunderstorm development. Rain and thunderstorm chances will
then expand across the CWA Thursday afternoon into the evening as
low pressure pushes northeast across the state. In terms of
coverage...Not expecting widespread coverage, but instead scattered
as low pressure spins up showers and storms throughout the day.
Copious amounts of moisture will remain in place as PW holds between
1.80 - 2.00 inches, which will translate to heavy downpours for
showers and storms that develop. Due to sporadic coverage, went with
40 - 60 PoPs for bulk of the day. Severe weather threat remains low
as CAPE, lapse rates, and bulk shear are lackluster.
As the low pushes northeast Thursday night into Friday morning,
northwest flow around the low will drag in a dry slot which will
briefly diminish rain chances late Thursday into early Friday
morning, especially closer to the Metro region as it will be further
removed from the low. Rain and low thunder chances again increase
late Friday morning into the afternoon as a PV anomaly over northern
Illinois weakens and pushes northeast into SE MI. Otherwise, Friday
will feel quite muggy as dewpoints rise into the mid to upper 60s,
with temperatures capped in the lower 80s for a high. Rain chances
are expected to end Friday afternoon into evening as the low moves
into New England, allowing high pressure to settle in across the area
from the north.
A dry period from Saturday through Monday looks likely as heights
slowly build aloft and weak high pressure fills in at the surface.
Highs near normal and light winds will result in pleasant conditions
for outdoor activities, though dew points in the lower 60s will keep
a mugginess in the air.
Next chance for precipitation comes late Monday into Tuesday. A
potent shortwave trough is progged to track from the Rockies through
the mid-Mississippi Valley and lift into the Great Lakes by early
Tuesday. A second trough is advertised to dig in from the Canadian
Prairie provinces later on Tuesday. Model guidance continues to
diverge on the strength and positioning of the resultant surface
feature. The ECMWF is still hinting at a sub-1000 mb surface low
developing and tracking northeast through Lower Michigan while the
GFS is currently advertising an elongated area of weaker low
pressure tracking just east of us - still with plenty of
precipitation on its western flank. Will continue to monitor trends
in the interaction of these upper troughs, but for now Southeast
Michigan can expect a decent chance of rainfall late Monday and
through the day Tuesday. Highs will remain near normal, though
potentially a few degrees cooler on Tuesday due to precipitation and
cloud cover. High pressure will begin to build in on Wednesday and
bring the return of quiet weather.
MARINE...
Stalled frontal boundary remains over northern Lake Huron this
afternoon producing light winds over much of the lake. A low
pressure system will be tracking northeast tonight and Thursday
passing over the eastern Lakes late Thursday. Showers and
thunderstorms will accompany the low tonight through Thursday night.
Southerly winds ahead of the low and south of the trough, will
become northerly across much of Lake Huron as the trough settles
southward tonight. Winds will become northerly by Friday behind the
low as it exits east but should remain below 20 knots keeping waves
in check.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
AVIATION.....CB
DISCUSSION...AM/TF
MARINE.......BT
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1019 PM EDT Wed Aug 15 2018
.UPDATE...
Issued at 1019 PM EDT WED AUG 15 2018
As expected, upstream convection has weakened as the outflow has
outrun the better radar returns. Based on present trends and
latest hi-res model output, rest of the night is shaping up to be
dry. Still lots of thinness in the clouds out there, so valley fog
should develop as we head through the night, especially with
dewpoint depressions already near zero in the valleys.
UPDATE Issued at 757 PM EDT WED AUG 15 2018
Last of the showers starting to pull out of eastern Kentucky and
dissipate as anticipated. This will provide a lull into the
overnight hours. Clouds have thinned out quite a bit this evening
and should allow some form of valley fog to develop overnight.
Thus, will include that with this update. We are watching a line
of storms crossing into central Kentucky, but this line should
weaken as it tries to push east and outruns the better instability
axis to our west.
UPDATE Issued at 507 PM EDT WED AUG 15 2018
Updated to bring pops farther to the east as we have had shower
activity along the trough axis shifting east across the area this
evening. This should only affect the area over the next few hours
before it dissipates or moves on out of the area. Quieter weather
will be seen overnight and may look to add some valley fog pending
the resulting cloud cover after the current activity moves out.
Future update will tackle this potential.
&&
.SHORT TERM...(This evening through Thursday night)
Issued at 414 PM EDT WED AUG 15 2018
The current surface map shows high pressure moving off to the
east through this evening. This has brought in southerly flow,
leading to the development of a line of showers in central
Kentucky early this afternoon that have progressed into eastern
Kentucky. There is the possibility of a few thunderstorms through
this evening as well, but instability is limited. Currently the
line looks to be breaking up somewhat, but lightning has been
detected near the Tennessee border.
An upper level shortwave trough as well as a surface cold front
will advance towards the Ohio Valley Thursday. This will bring
likely chances of showers and also the potential for thunderstorms
for all of eastern Kentucky. With the potential for heavy
rainfall, there is a risk for flash flooding Thursday into Friday.
Utilized the CONSShort and the HRRR as a baseline, along with
current radar trends, for PoPs into this evening. Models are in
good agreement with the overall pattern for the system Thursday
into Friday. Stuck with the Blend`s timing and progression for
this system. High temperatures will be in the mid to upper 80s and
low temps will generally be around 70.
.LONG TERM...(Friday through Wednesday)
Issued at 401 PM EDT WED AUG 15 2018
The extended forecast begins on Friday with an active pattern
expected with a chance of rainfall expected nearly everyday of the
extended. On Friday, the day will begin with an approaching upper
wave as a weakened surface cold front pushes southeast through
the area. Increased moisture flow with high pressure to the east
and southerly flow in place, will expect showers and thunderstorms
to develop for the day Friday. Model soundings suggest a bit
higher storm motion winds so any flood threat will result from
training thunderstorm cells. With lingering high pressure over the
southeastern CONUS the southern end of the front will stall over
eastern Kentucky keeping the boundary over the eastern portion of
the state through the weekend. Along with this setup, numerous
disturbances will track across This combined with ample moisture
everyday will keep the chance for precip in the area through the
weekend. Depending on storm motion and the potential for training
storms will drive the potential for flooding.
Heading into Monday and Tuesday, another feature will follow
behind the front from the weekend with once again again, good
southerly flow and decent instability developing each afternoon.
This is expected to be another situation with good afternoon
convection once again bringing the chance for some heavy rainfall
each afternoon. Overall, an active and wet period is expected
through nearly the entire extended forecast period.&&
.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 211 PM EDT WED AUG 15 2018
A line of showers in central Kentucky has progressed into the
Cumberland Basin early this afternoon. It will make its way
northeast across the Commonwealth through this evening and affect
most TAF sites. However, SJS is not expected to be affected by
these showers today. A few embedded thunderstorms are a
possibility this afternoon/evening, but confidence is low in the
amount of instability available. Therefore, have left mention of
thunder out of the TAFs at this time. Winds will generally be 5
knots or less out of the south. However, winds will begin to
increase with the approach of a cold front tomorrow afternoon.
&&
.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 211 PM EDT WED AUG 15 2018
A line of showers in central Kentucky has progressed into the
Cumberland Basin early this afternoon. It will make its way
northeast across the Commonwealth through this evening and affect
most TAF sites. However, SJS is not expected to be affected by
these showers today. A few embedded thunderstorms are a
possibility this afternoon/evening, but confidence is low in the
amount of instability available. Therefore, have left mention of
thunder out of the TAFs at this time. Winds will generally be 5
knots or less out of the south. However, winds will begin to
increase with the approach of a cold front tomorrow afternoon.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...KAS
SHORT TERM...CGAL
LONG TERM...SHALLENBERGER
AVIATION...KAS
Area Forecast Discussion
National Weather Service Louisville KY
1103 PM EDT Wed Aug 15 2018
.Forecast Update...
Issued at 1100 PM EDT Wed Aug 15 2018
Already seeing a second round of showers/storms forming as 30-40
knot low-level jet is cranking at the PAH/VWX/LVX VAD wind profiles.
Decided to go ahead and fire up a small area Flash Flood Watch for
the overnight...based partly on where the earlier rains fell as well
as where the HRRR and 00Z NAM and ARW place new convection
overnight.
Issued at 1010 PM EDT Wed Aug 15 2018
Portions of southern Indiana and north central Kentucky received 0.5
to 1.5 inches of rain from storms this evening. The main forecast
concern overnight is additional rainfall depicted by the NAM/HRRR.
With PWATs rising to just over 2 inches and a good LLJ tonight
through tomorrow morning, anticipate showers with embedded storms
overnight to put down a good amount of rainfall likely in the same
axis that received a good soaking this evening. Debated with
surrounding offices on a Flash Flood Watch overnight but could not
come to a consensus. Decided to pass along to the midnight shift
that will evaluate 0Z data and determine our FF risk for the rest of
tonight through tomorrow.
&&
.Short Term...(This evening through Thursday)
Issued at 305 PM EDT Wed Aug 15 2018
...Get your umbrellas ready...very wet period ahead...
Well...Lots of clouds keeping temps down today with upper low over
Show Me State. Ahead of this system, there is a warm sector with dew
points in the lower 70s. Currently, there is scattered shra and
isolated tsra over S IN while we await for new convective
development from NW TN to SW KY. This will spread into our area late
this afternoon from strong sfc heating. Strong warm air advection
pattern is setting up later today with low level jet of 30-40 kts.
This will set up excellent efficient isentropic lift across area
after 00z especially late evening into overnight. This will yield a
high POP widespread rain event with isolated tsra with locally heavy
rainfall, especially west of I-65.
PWATs will increase to 1.75 to as high as 1.9 inches with the
isentropic lift, so there will be pockets of heavy rain. The ground
is fairly dry so not even thinking of any headlines at this
juncture. However, locally embedded high efficiency convection could
cause some isolated issues. The Weather Story messaging will keep
talking about potential for locally heavy rainfall.
High temp Thursday will be below normal with so much cloud cover.
Lower 80s seems prudent especially west of I-65.
.Long Term...(Thursday night through Wednesday)
Issued at 300 PM EDT Wed Aug 15 2018
...Multiple episodes of showers and storms to continue through the
extended period, with a possible break on Sunday...
Thursday night and Friday...
As an initial shortwave trough aloft moves to our east Thursday
night, a deeper trough will swing southeast through the mid and
upper MS Valley. Residual showers and storms associated with the
initial trough may move away or become fewer in number Friday
evening. However, forcing ahead of the approaching trough combined
with a continued moist air mass and suggestion of steepening mid-
level lapse rates should allow for additional convection to form
somewhere over the lower OH Valley (probably initially west of our
area), then move east into at least parts of central KY and south-
central IN late Thursday night/Friday morning. This activity could
last into the daytime Friday, with any outflow boundaries dictating
where additional cells may develop Friday afternoon and evening.
These storms should produce high rainfall rates, so coupled with
earlier rains and if cells repeat over the same areas, localized
flood concerns could occur. Highs Friday will be in the lower and
mid 80s, depending on amount of cloud cover.
Friday night through Sunday...
During this period, the trough aloft will move east and weaken but
may be unable to create a "clean sweep" of the moisture and precip
chances to our east. A weak surface boundary will work its way
slowly south across the lower OH Valley Friday night and Saturday.
Model soundings show that at least marginal to perhaps moderate
instability will remain over much of the forecast area through at
least Saturday. While areal coverage of precip will diminish,
isolated to scattered showers and storms are still possible during
the forecast period, especially over central KY. The frontal
location suggests that precip chances may end over south-central IN
Saturday night and Sunday, but with still a chance for isolated
cells Sunday over central KY. Expect high temps Saturday and Sunday
to range through the 80s.
Monday through Wednesday...
Yet another significant shortwave is forecast to dig southeast
across the central U.S. Monday with southwest flow aloft developing
over the OH Valley. Besides renewed instability, this system
actually could have some deep-layered shear associated with it for
some strong convection, at least to our west over parts of the mid
MS and lower OH Valleys on Monday. Storms would then work into our
forecast area late Monday/Monday night and could linger or redevelop
under the upper trough on Tuesday. If the current forecast holds,
drier, less humid air would spread into our area Tuesday night and
Wednesday.
&&
.Aviation...(00Z TAF Issuance)
Issued at 805 PM EDT Wed Aug 15 2018
The main TAF concern will be multiple rounds of showers and storms
as multiple upper level disturbances pass through the region ahead
of an upper trough. SDF will be affected within the next hour with
strong t-storms with gusts to 50+ mph possible and IFR conditions.
After this storm passes SDF should see mainly showers with a few
rumbles of thunder for the rest of the night like HNB. Showers and
storms will be slow to arrive at BWG/LEX late tonight into tomorrow
morning. Look for more rounds of showers and storms to affect all
TAF sites throughout the day tomorrow. In addition, SSW winds of 8-
12kts will gust to around 18-22 kts tomorrow afternoon/evening.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Flash Flood Watch through Thursday afternoon for INZ077>079-084-
089>092.
KY...Flash Flood Watch through Thursday afternoon for KYZ023>025-
028>033.
&&
$$
Update...RJS/AMS
Short Term...JDG
Long Term....TWF
Aviation...AMS
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1102 PM CDT Wed Aug 15 2018
.UPDATE...
Issued at 1055 PM CDT Wed Aug 15 2018
Updated to include 06z aviation discussion below.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 412 PM CDT Wed Aug 15 2018
We have seen scattered thunderstorms develop this afternoon on
the remnants of the cold front that moved into southern MN
yesterday. Thunderstorms have basically been confined to where
surface dewpoints have stayed up near or above the 70 degree mark.
RAP analysis shows areas with 70 degree dewpoints have managed to
develop 1500-2000 j/kg of MLCAPE. Given the weak surface flow,
this zone of higher moisture/instability will not move much, which
means the showers we are seeing develop this afternoon will
basically stay where they are, along and south of a Mankato to Eau
Claire line.
For tonight, winds will be calm, which means we will have to
chase radiational fog once again. The couple of factors that will
drive the fog is the extent of cloud cover we see from the wave
currently moving along the SD/Neb border, with the other being
whether or not we have enough time to hit our cross-over temps.
Looking at dewpoints this afternoon, cross-over temps will range
from the upper 50s in central MN to the upper 60s from south
central MN into central WI. CAMS and MOS guidance really favoring
south central MN up into western WI and across central up into
northeast MN as having the biggest threat for seeing fog. For now,
have patchy/areas of fog mention in the grids, but would not be
at all surprised if we ended up with a dense fog advisory for
parts of the area tonight.
Thursday, the upper low currently in SoDak will scoot across IA,
so the greatest coverage in precip is expected to our south.
However, with weak low level flow, we won`t see much of a change
in the surface dewpoint pattern, which means where we are see
scattered showers today will have the threat of a repeat
performance Thursday.
.LONG TERM...(Thursday night through Wednesday)
Issued at 412 PM CDT Wed Aug 15 2018
The long term still features one good hope for widespread
beneficial rains Sunday and Monday. We`ll also get a couple of
more opportunities to touch 90 for a high Friday and Saturday,
with highs falling back into the 70s with the rain and clouds
Sunday and Monday. We`ll see northwest flow briefly behind this
wave, with highs remaining around 80 as skies clear out going into
the middle of next week.
Only change to the forecast Friday and Saturday was to go above
blended guidance for highs. As we have seen since the weekend, as
the ground continues to dry out, we are getting more and more
efficient at warming up on these mostly sunny days, which Friday
and Saturday will certainly be. In fact, Friday and Saturday will
offer the Twin Cities two more chances at hitting 90. Currently,
MSP sits at 18 90+ days this summer. If we were to push the count
to 20, it would be the first time we topped 20 90+ days in a
summer since 2012 when we had 31.
For Sunday and Monday, models appear to be honing in on a
solution of bringing us our most significant rains on a more
widespread basis since the 3rd and 4th. Where uncertainty comes in
is this still looks to feature the phasing of a southern stream
system with the northern stream, which this far out is always
tricky to pin down the exact details on. At the moment, it is
looking like the northern stream will be sending a cold front
across NoDak Saturday, with rain moving into west central MN
Saturday night. Sunday, an upper circulation coming out of the
central Rockies will be moving across Iowa before getting swept
into the northern stream Monday over the Great Lakes. As this wave
is moving across IA, it will be deepening, with deformation to
the northwest of the low strengthening. It`s the fgen associated
with the deformation that will help force a prolonged light precip
event across our area on Monday. Our PoPs could certainly be
higher, though we`ve seen several for sure rain events 5 days out
evaporate to almost nothing by the day of this month, so we were
alright with sticking with the high chance/low likely pops
SuperBlend gave us, even though what we are seeing now would
suggest we could be higher with pops.
Behind this system, we`ll see northwest flow develop, which will
give us sun and mild temperatures Tuesday and Wednesday before we
start warming again at the end of next week.
&&
.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1055 PM CDT Wed Aug 15 2018
Mainly VFR conditions expected throughout this TAF set though
there is decent potential for pre-dawn fog in eastern MN through
western WI. Winds will likely go calm in these areas along with
little to no dewpoint depressions, especially near spots which
received rainfall. Have included/maintained fog mention for MSP
southward and eastward with much lower chances west and north of
MSP. No precipitation expected at any of the TAF sites.
KMSP...Some potential for MVFR fog around time of the morning push
but, at this point, am not expecting fog to reduce visibility less
than 5SM. Upper level ceilings then expected through the middle
portion of the day tomorrow before scattering out late.
/OUTLOOK FOR KMSP/
Fri...VFR. Wind NW 5 kts.
Sat...VFR. Wind S 5 kts.
Sun...Chc -SHRA/-TSRA/MVFR afternoon on. Wind S 5-10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&
$$
UPDATE...JPC
SHORT TERM...MPG
LONG TERM...MPG
AVIATION...JPC
Area Forecast Discussion
National Weather Service Raleigh NC
947 PM EDT Wed Aug 15 2018
.SYNOPSIS...
An upper-level ridge will extend into the region through
Thursday, resulting in warmer weather with limited rain chances.
A cold front will approach the region over the weekend resulting
in a return to unsettled weather.
&&
.NEAR TERM /TONIGHT/...
As of 945 PM Wednesday...
00Z upr air data indicate a ridge at 500 mb has closed off over VA
this evening. A weak shear axis stretching west to east over cntl NC
separates this high from a pair of parent sub-tropical ridges
centered over srn TX and Bermuda, respectively. A higher
level/shallow perturbation, centered in WV satellite data over sern
TN/nwrn GA, will drift esewd across the srn Appalachians and into w-
cntl SC/ern GA by Thu morning. Given how shallow this feature is and
that it will be moving into a region otherwise dominated by weak mid-
upr level height rises, no appreciable lift or impact is expected
ahead of this feature, aside from perhaps some enhancement of cirrus
already streaming across the Carolinas.
At the surface, a trough stretching from ern NC swwd across cntl SC
and s-cntl GA was again analyzed as a (quasi-stationary) front at
22Z because of the 7-10 degree dewpoint difference across it, though
it has again become less apparent in surface observational data
since that time owing to both nocturnal surface dewpoint recovery
and the inland retreat of the sea breeze. The boundary was analyzed
as a warm front from cntl GA nwwd across cntl TN and w-cntl KY,
where it intersected composite outflow/ongoing convection.
Low level convergence along the front and nearby outflow --in the
same areas as last evening, from the NC srn Piedmont enewd across
the Sandhills and srn-cntl Coastal Plain-- and amidst ~1000-1500
J/kg of MLCAPE per 00Z RAOB data at MHX (1000 J/kg) and CHS (1900
J/kg), will favor continued isolated to widely scattered shower
development until around midnight, after which time nocturnal
cooling and related weakening CAPE and strengthening CINH should
become too great to overcome, in the absence of any larger-scale
support for lift.
Considerable high cloudiness may keep temperatures from reaching
full radiational cooling potential and likewise limit fog
development. However, recent HRRR runs and the 21Z SREF both favor
the Sandhills and Coastal Plain for any such fog or low stratus
development early Thu morning; which seems reasonable given that
will be where moisture/convergence will be maximized near the front
once again. Lows are expected to range from mid-upr 60s over the nrn
Piedmont to lwr 70s along and southeast of the front.
&&
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 315 PM Wednesday...
Bermuda high pressure will gradually build westward into the SE US
Thu and Thu night. The rising mid/upper level heights and associated
subsidence will limit convective development. Still, a persistent
low level trough may provide enough of a focus for moisture to pool
to permit an isolated shower or two to develop. This threat appears
greatest across our southern counties. Overall, most locations will
remain dry. The subsidence aloft will warm the atmosphere, leading
to afternoon temperatures a couple of degrees warmer than this
afternoon. This will yield high temperatures in the low and mid 90s.
With sfc dewpoints in the upper 60s to around 70, heat indices will
be well into the 90s, approaching 100 degrees across portions of the
Sandhills and Coastal Plain.
Isolated convection will dissipate with loss of heating, leaving in
their wake partly cloudy skies. Dewpoints will be inching upward as
the low level flow gradually increases from the south. Overnight
temperatures, in turn, will be a tad warmer, ranging between 70-75.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 210 PM Wednesday...
After a few days of relatively quiet and inactive weather, the
weather pattern will become increasingly unsettled into the
weekend.
The upper-level ridge across the sub-tropical Atlantic shifts south
slightly as troughing over the upper Midwest on Friday shifts
east. A positively tilted, sheared upper trough will extend
from the Northeast down across the Appalachians on Saturday and
then shift toward the coast on Sunday. An associated cold front
stretching from the New England States into the OH valley on
Saturday will drop into the Mid-Atlantic on Sunday. Convection
should be widely scattered on Friday but as the upper-level
trough approaches on Saturday and shifts overhead on Sunday, the
pattern will support greater than typical chances of mainly
afternoon and evening showers and thunderstorms over the
weekend. The flow aloft strengthens on Saturday with 0-6km bulk
shear values ranging near 20kts which could support stronger
and more organized storms. Additionally, precipitable water
values will approach 2 inches on Saturday and increase further
on Sunday, supporting convection with locally heavy rain. Max
temperatures should be the greatest on Friday with more limited
storm and cloud coverage with morning low-level thickness values
in the 1415-1420m range with highs ranging from 89 to 94. Highs
will relax into the 87 to 92 range on Saturday and the 85 to 90
range on Sunday with morning lows in the 68 to 75 range each
day.
A transient short wave ridge arrives on Monday in between the
departing trough off the coast and an approaching trough across
the mid-Mississippi Valley. In addition, the stalled front near
the NC/VA border should lift north which should result in more
widely scattered convection. As the upper-trough sharpens and
the associated cold front approaches late Tuesday into
Wednesday, shower and thunderstorm chances will once again
increase. Highs will range in the upper 80s to lower 90s with
lows within a few degrees of 70 each day.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 810 PM Wednesday...
VFR conditions are highly likely at all locations through at least
07z tonight. Showers will continue near FAY for another hour or so
(until 01z or 02z), and RWI may see a brief sprinkle during this
time, but VFR conditions should be maintained. After 07z, areas
along and east of a weak surface trough may see a period of MVFR
vsbys in light fog, with FAY and RWI the most likely to be
prevailing MVFR 08z-13z. VFR conditions will then return at all
locations, and persist through the end of the TAF valid period. FAY
and perhaps RWI may see another quick shower late Thu (20z-00z).
Looking beyond 00z Fri, apart from a chance of MVFR fog 08z-13z Fri
morning, VFR conditions will likely hold through Fri, although there
will be a better chance of showers/storms Fri afternoon as compared
to today/Thu. The shower/storm chance will extend through Fri night
and Sat, with possible sub-VFR conditions, including early-morning
fog Sat. Greater-than-usual shower/storm coverage is expected Sat
through Mon, with a higher risk of sub-VFR conditions, as deep
moisture returns to the area. -GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Blaes
NEAR TERM...MWS
SHORT TERM...WSS
LONG TERM...Blaes
AVIATION...Hartfield
Area Forecast Discussion
National Weather Service Tucson AZ
131 PM MST Wed Aug 15 2018
.SYNOPSIS...A moist atmosphere will result in scattered to numerous
showers with embedded thunderstorms through Thursday along with
cooler temperatures. A fairly typical monsoon pattern is expected
this weekend into early next week with temperatures near to slightly
above normal.
&&
.DISCUSSION...It;s quite moist out there today with PWAT values
ranging from 1.25 inches for eastern areas to 1.75 inches across the
western deserts. Latest visible satellite imagery shows the
leftover MCV from convection overnight over western Pima County
pushing northward. Meanwhile, there a mid/upper level inverted
trough is also present across southwest Arizona as well. On the
eastern flank of the inverted trough we`ve seen considerable shower
activity primarily across far eastern Pima County into western
Cochise County. While the showers have been persistent most locales
have seen less than 0.25" over the last 6 hours with just some
isolated higher amounts. The atmosphere is largely worked over and
thus limiting surface based convection across the Tucson Metro area,
but the same can`t be said closer to the international border of
Santa Cruz and Cochise counties where showers and thunderstorms have
been developing over the past couple of hours. Latest runs of the
HRRR and the 15Z UOFA WRF-RR seem to have the best handle on what is
a complex situation across the region. We expect that the shower
activity across eastern Pima County will generally decrease this
afternoon but renewed scattered shower and thunderstorm development
will continue especially south and east of Tucson. The main concern
today given the very moist atmosphere is heavy rainfall and flooding
issues, especially for areas that got hit with heavier rain last
night. Shower activity should generally diminish this evening
through the overnight but with this much moisture we do tend to lose
some of the diurnal characteristics of the precipitation.
A similar setup is on the table for Thursday with deep moisture
remaining across southeast Arizona but with very weak southerly flow
as the mid level high is just east of the area. Much will depend on
how much solar insolation there is on Thursday but the potential
will once again exist for scattered to numerous thunderstorms with
locally heavy rain. The storms may tend to favor the higher terrain
given the slow steering flow.
Thereafter, deep moisture will remain on Friday as the flow becomes
a bit more northeasterly. The mid/upper level high will
reconsolidate to our northwest this weekend with a northeasterly
flow persisting Saturday. There is some indication that moisture
will be lessening as early as Saturday but in particular on Sunday.
While this won`t shut the monsoon down, it will keep the best
chances of precipitation from Tucson south and eastward. By early
next week, the mid/upper level high will setup across northern New
Mexico into Arizona with a more easterly steering flow. Perhaps some
increased moisture around Monday and Tuesday but then a possible
downward trend in activity as the high shifts more overhead. Still
lots of uncertainty that far out with the bottomline being some
thunderstorm chances everyday in at least portions of southeast
Arizona through the forecast period.
Temperatures will be below normal through Thursday before warming up
and being near to even slightly above normal levels Friday into
early next week.
&&
.AVIATION...Valid through 17/00Z.
Isolated to scattered -SHRA/-TSRA will continue through the evening
hours just east of KTUS and to the south along the international
border. Storms will start to dissipate around 16/04Z. Isolated to
scattered -SHRA/-TSRA will again be possible tomorrow afternoon from
Tucson eastward. Brief MVFR conditions possible with the -TSRA,
otherwise SCT-BKN cloud bases generally 8-12k ft AGL this evening
and tomorrow afternoon. Tonight expect SCT-BKN clouds AOA 20k ft AGL
from leftover debris clouds. Outside of thunderstorm gusts, expect
SFC winds mainly less than 12 kts. Aviation discussion not updated
for TAF amendments.
&&
.FIRE WEATHER...The pattern is favorable for scattered showers and
thunderstorms into this weekend, but there are hints of drier
conditions by Sunday. Near or slightly below normal temperatures
will continue through the forecast period. 20-ft winds will be
terrain driven at less than 15 mph, except for in and around
thunderstorms where strong outflows may occur.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
PUBLIC...Lader
AVIATION/FIRE WEATHER...Hardin
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