Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/20/17
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
758 PM CDT Wed Jul 19 2017
.UPDATE...
Issued at 757 PM CDT Wed Jul 19 2017
Allowed the heat advisory to expire as temperatures have fallen
into the 70s and 80s across the region this evening.
UPDATE Issued at 635 PM CDT Wed Jul 19 2017
Amended pops for the rest of the night. Removed pops from James
valley west except for south of I-90. Still have some slight
chances for showers and thunderstorms for the southeastern cwa
later this evening, including Watertown, because of the decent mid
to upper level dynamics.
&&
.SHORT TERM...(This Evening through Thursday Afternoon)
Issued at 307 PM CDT Wed Jul 19 2017
Forecast challenges include when/where any convection may initiate
late this afternoon/early evening along with temperatures.
Currently, rain-cooled stable boundary layer air resides across the
northeastern two-thirds of the cwa, with readings still only in the
60s this afternoon over the Prairie Coteau over into west central
MN. Further south and west towards the Pierre area, temperatures are
beginning to nudge their way closer to the lower 90s this afternoon.
As far as heat indices go, the rain-cooled boundary layer hasn`t
depleted the low level moisture any. Dewpoints are still in the
upper 60s to low 70s across the region, but where temps are no
longer expected to reach up into the upper 90s to low 100s, heat
indices in the advisory area will only reach the marginal range at
best, except for an area south of a line from Mission Ridge to Gann
Valley where the combination of hot temperatures and high dewpoints
should be able to push heat index readings up to 100 or better for a
couple hours late this afternoon/early this evening. Also, just
about all the convection from earlier today has pushed off into
Minnesota.
Rest of this afternoon through late this evening: given the degree
of boundary layer stabilization that has occurred across northeast
South Dakota and west central MN today, not really expecting much in
the way of surface-based convective activity there over the next 6
to 12 hours. If convection does re-develop across that area, it
would be elevated in nature and forced mainly from a combination of
strong mid-level waa/moisture advection and upper level jet
enhancement. Can`t rule out a strong storm or two there (large hail)
from super-cellular elevated cells. The more probable region over
this cwa for convection rooted/nearly rooted in the boundary layer
is the far southwestern zones (I-90 corridor) where less influence
from stabilizing effects of morning outflow exist. Capping inversion
is being eroded and instability/shear off the Rap Refresh model has
an instability gradient of 1000 to 4000J/kg of CAPE positioned over
Lyman County where 0-6km bulk shear is 30 to 55 knots. If storms do
initiate or move into far southwestern zones, very large hail and
strong/damaging winds would be the primary severe weather threats.
Late tonight through Thursday: much of the rest of tonight and
Thursday should be quiet, dry and warm while the cwa is in between
mid-level shortwaves and under the influence of surface high
pressure and northeasterly boundary layer winds.
.LONG TERM...(Thursday Evening through Wednesday)
Issued at 307 PM CDT Wed Jul 19 2017
The meandering frontal boundary will return back north across our
forecast area Thursday night. This will be while 2 areas of low
pressure organize across western ND and western NE by daybreak
Friday. While still divided, much of the precipitation will likely
slide to our north or south. For Friday night-Saturday, expect much
of the activity to our north, closer to the 500mb low crossing south
central Canada. The only time with confidence to put chance pops in
the forecast was overnight Thursday night-Friday morning, and again
Friday evening.
Expect dry weather to return to the region Saturday through Monday
morning. The 500mb ridge looks to slowly build back overhead towards
the end of the weekend into early next week. The main fly in the
ointment is another 500mb low crossing central Canada midweek. The
12Z GFS is the farthest south with the track, suppressing the ridge
Tuesday-Wednesday. Still, confidence is high that we`ll still
experience temperatures in the 80s and 90s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 635 PM CDT Wed Jul 19 2017
VFR conditions and light winds are expected through the period
except in the vicinity of thunderstorms. KATY is the only site
that has a chance of seeing some showers and thunderstorms this
evening because of good upper level dynamics.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory until 8 PM CDT /7 PM MDT/ this evening for SDZ033-
035>037-045-048-051.
MN...None.
&&
$$
UPDATE...Wise
SHORT TERM...Dorn
LONG TERM...KF
AVIATION...Wise
Area Forecast Discussion
National Weather Service Albany NY
955 PM EDT Wed Jul 19 2017
.SYNOPSIS...
Warm temperatures will continue through the next few days.
Chances for thunderstorms will increase late Thursday into
Thursday night, mainly for areas south of Albany. High pressure
will build in from the Great Lakes Friday into Saturday with dry
conditions and near normal temperatures.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
As of 1000 PM EDT...Mesoscale window from SPC suggests a small
pocket of mid level instability tracking across the St
Lawrence Valley where some showers/storms were ongoing through
this early evening where lapse rates where near 6.5 C/KM. The
mean mid level flow remains from the west so the deeper
convective elements should remain north of our Dacks. Otherwise,
diffuse frontal boundary was moving across the region from
northwest to southeast. So per the latest HRRR and RAP13
guidance we will keep the tonight portion of the forecast dry.
Some patchy valley fog may develop again in favored areas near
warm bodies of water, although coverage should not be extensive
due to better mixed environment compared to last night. Min
temps should be in the 60s across much of the region.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
Much of Thursday should feature tranquil weather and continued
warm temperatures as a small ridge of high pressure builds in.
Dewpoints will creep back up in the mid to upper 60s, making it
feel more humid compared to Wednesday.
The main question/forecast challenge will be late Thursday into
Thursday night, with regards to convective potential. Models
have trended farther south with a potential cluster of showers
and thunderstorms propagating from the Great Lakes region. With
an upper level ridge firmly entrenched across the central CONUS,
thinking is that convection over the western Great Lakes region
will track more southeast than eastward, following the better
instability and flow around the large ridge in the central
CONUS. Instability parameters from the NAM/GFS showing higher
values to the south and west of our area. There could be enough
CAPE around 500-1000 J/Kg to sustain isolated to scattered
convection across southern portions of the area, but potential
for severe storms has decreased compared to earlier forecasts.
The Storm Prediction Center has scaled back the Slight Risk
area to just include parts of the eastern Catskills, with
reduction to Marginal Risk for much of the rest of the region.
This trends agrees with our thinking as well, but due to low
confidence forecast in the zonal flow aloft will continue to
monitor trends closely.
Tranquil weather looks to return for Friday, as high pressure
over the Great Lakes builds eastward into the Northeast.
Temperatures will be slightly cooler, but still a bit above
normal. Further cooling with lower humidity levels expected
Friday night high pressure gets closer.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
We begin the forecast period with high pressure nosing into our
region from Canada with a warm front associated with a system
in the Great Lakes trying to edge its way from the mid -
Atlantic into the Northeast. The main forecast challenge here
is determining how long the high can suppress the front to the
mid
- Atlantic before it finally pushes northward. At this time,
guidance suggests that the first half of Saturday should be
mainly dry for our CWA; however, H850 winds become perpendicular
to a decent H850 thermal gradient situated over our southern
CWA for the afternoon on most of the guidance so have increased
POPs and thunder threats then. BUFKIT soundings do suggest that
there is decent mid level dry air that the WAA will have to
overcome so have kept the highest POPs limited to our far
southern counties and decreased POPs heading NW.
The front and associated WAA should strengthen Saturday night
into Sunday but again how far north it can go is still
uncertain. The Canadian model in recent weeks has done a good
job identifying precipitation shields and it has shown in recent
model runs the northern extent of the precipitation shield
stays limited to coastal CT/NYC and our southern counties for
Saturday night into Sunday. The Euro on the other hand delays
precipitation until daytime Sunday and suggests more of our CWA
receiving measurable rainfall as a low rides along the front.
These set ups are tough to get right this far in advance so for
the time being have given the highest POPs for daytime Sunday
with the highest POPs in the southern tier of the CWA and gave
low chance POPs heading north. Also temperatures on Sunday look
to be a few degrees below normal in the 70s.
The front and the unsettled pattern stays in place Monday and
Tuesday. Our front stays in the vicinity of coastal CT/NYC and
an impressive shortwave trough from the Great Lakes swings into
the Northeast, potently becoming negatively tilted. Guidance
shows a disturbance developing along the boundary as a result of
the PVA from the shortwave but again which areas are impacted
from the disturbance will be dependent on where the front set
ups. Most of the guidance at this junction show the low
impacting coastal New England but this likely will shift with
each new model run so the Monday-Tuesday time period is a low
confidence forecast.
The shortwave should be out of the area by mid-week with
Canadian high pressure and a drier pattern building into the
region. Temperatures could be near to slightly below normal
during this time in the upper 70s for highs and 50s for
overnight lows.
&&
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Mainly VFR through the evening hours under a mixture of SCT-BKN
mid and high clouds. As surface frontal boundary slides through
the region, winds relax to allow for some fog to develop late
tonight however not as much as the last couple of nights as we
did not get any rain today and good mixing through the daylight
hours. If we do see flight restriction, MVFR conditions
at KGFL and KPSF overnight. Any fog will burn off quickly after
sunrise. Diurnal cumulus will once again form with daytime
heating.
Winds will diminish this evening becoming light to calm for the
overnight. A westerly flow will develop once again Thursday,
however the flow will be more southerly at KGFL due to local
effects.
Outlook...
Thursday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Friday: No Operational Impact. NO SIG WX.
Friday Night: No Operational Impact. NO SIG WX.
Saturday: No Operational Impact. NO SIG WX.
Saturday Night: Low Operational Impact. Slight Chance of SHRA...TSRA.
Sunday: Moderate Operational Impact. Chance of SHRA.
Sunday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Monday: Moderate Operational Impact. Chance of SHRA...TSRA.
&&
.FIRE WEATHER...
Warm temperatures will continue through the next few days. Chances
for thunderstorms will increase late Thursday into Thursday night,
mainly for areas south of Albany. High pressure will build in from
the Great Lakes Friday into Saturday with dry conditions and near
normal temperatures.
Relative humidity values will increase to around 90 to 100 percent
tonight, dropping to minimum values of 40 to 50 percent on Thursday.
RH will increase to between 90 and 100 percent again Thursday night.
Winds tonight will be westerly around 5 mph or less. Winds on
Thursday will remain west and increase to 5 to 10 mph on Thursday.
Westerly winds will continue Thursday night around 5 mph.
&&
.HYDROLOGY...
Dry conditions will persist tonight through much of Thursday.
Chances for showers and thunderstorms will then increase late
Thursday into Thursday night, as an upper level disturbance moves
through the region. Still uncertainty regarding the placement, but
at this time it appears areas south of Albany have the greatest
potential for a few downpours. Storms expected to move relatively
quickly, so no flooding is anticipated at this time.
Dry weather will return Friday through Saturday with high pressure
building in. Then, another bout of wet weather with additional
showers and thunderstorms is expected from Sunday through early next
week.
For details on specific area rivers and lakes, including
observed and forecast river stages and lake elevations, please
visit the Advanced Hydrologic Prediction Service /AHPS/ graphs
on our website.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.
&&
$$
SYNOPSIS...JPV
NEAR TERM...BGM/JPV
SHORT TERM...JPV
LONG TERM...Speciale
AVIATION...IAA/BGM
FIRE WEATHER...NAS
HYDROLOGY...JPV/JVM
Area Forecast Discussion
National Weather Service Grand Forks ND
931 PM CDT Wed Jul 19 2017
.UPDATE...
Issued at 931 PM CDT Wed Jul 19 2017
No updates needed.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 325 PM CDT Wed Jul 19 2017
Latest HRRR which has performed poorly with this event is finally
catching on the idea of little activity going in in our area as
the frontal boundary approaches from central ND. Quite a bit of
subsidence behind the main short wave trough is east of our area
inhibiting lift despite modest temp recover into the 75-80 range
in E ND and dew pts in the mid 60s. LAPS has cape into the
1500-2000 j/kg range into the RRV at 19z due to the temp/dew pt
combination and relative lack of capping, but very little in the
way of upper level support to get things going. Still though with
unstable airmass thru 00z will hang on to some low pops...and into
03z in the far southeastern fcst area. Severe risk is very
low...though updated day 1 SPC outlook kept far south in slight
risk. Clearing overnight. Mostly sunny Thursday with temps close
to the normal values and light winds as well due to high pressure
moving in.
.LONG TERM...(Thursday night through Wednesday)
Issued at 325 PM CDT Wed Jul 19 2017
Thursday night into Friday morning will see a short wave riding
over the 500 mb ridge and into the area developing tstms in W ND
late Thu aftn/eve and moving east-northeast into S Manitoba and
central/ern ND overnight. Lingering precip into Fri AM. Appears
best risk area for storms is near or just north of the Intl
border. Main frontal boundary will move through later Friday or
Friday night with models in rather poor agreement with timing and
when best chc of storms will occur. Most due have it Fri night
though and some severe risk is present. Day 3 SPC has much of the
area in marginal or slight risk. Upper level trough moves thru
Saturday with some chances for showers and t-storms, mainly north
and east.
Sunday through Wednesday...
The end of the weekend and start of the new work week looks to be
dry and quiet with surface high pressure taking hold of the region.
Cooler northerly flow following Saturday`s system should keep
temperatures down in the 70s for Sunday, even with some sunshine,
before warming back closer to 80 for Monday.
Models are in pretty decent agreement regarding the return of
precipitation chances late Monday and continuing through the end of
the period as temperatures warm back near normal values in the low
80s or so.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 638 PM CDT Wed Jul 19 2017
Expecting winds to decrease by sundown and remain pretty light for
the next 24 hours.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
&&
$$
UPDATE...Godon
SHORT TERM...Riddle
LONG TERM...Lee/Riddle
AVIATION...Godon
Area Forecast Discussion
National Weather Service Hastings NE
950 PM CDT Wed Jul 19 2017
.UPDATE...
Issued at 949 PM CDT Wed Jul 19 2017
Really only one noticeable modification has been made to the
overnight forecast:
Perhaps out of an abundance of caution more than anything, have
added some slight shower/thunderstorm chances (PoPs) to our far
north, mainly north of a Loup City-Genoa line. As expected, the
vast majority of late afternoon/evening thunderstorm activity
(including isolated severe weather) has remained slightly north
of our CWA in a west-east corridor across northern Nebraska.
However, there are signs both in radar trends and also models such
as the HRRR that at least weak elevated convection could try
brushing southward into our northern zones especially 11PM-4AM,
possibly aided by the increasing low level jet lifting over an
outflow boundary. Not anticipating anything severe, but some gusty
winds up to around 40-ish MPH probably cannot be ruled out.
Otherwise, the majority of the CWA should see a rain/thunder-
free night with seasonably-warm lows holding up in the low-mid
70s.
&&
.SHORT TERM...(This evening through Thursday)
Issued at 155 PM CDT Wed Jul 19 2017
Hot and humid conditions will continue across the local area
through the short term periods with little relief in sight ahead
of weak cold front across the Dakotas. As this front slowly sinks
south over the next 24 to 48 hours hours...expect the pressure
gradient to weaken across the region...likely resulting in
lighter winds across the local area tomorrow. While temperatures
as well as heat index values will be similar across the region
tomorrow as we saw today...these lighter winds will likely make it
feel a bit more miserable...with either a Heat Advisory or an
Excessive Heat warning in place for the entire forecast area.
.LONG TERM...(Thursday night through Wednesday)
Issued at 155 PM CDT Wed Jul 19 2017
A weak shortwave is expected to ride over a weak cold front to our
north Thursday night...possibly sparking some convection across
portions of northern Nebraska. While the best chance appear to be
north of the local area...cannot rule a few storms temporarily
bringing some relief to areas primarily north of highway 92 across
south central Nebraska late Thursday night.
Otherwise...expect strong high pressure to slowly give way to the
aforementioned cold front late Friday night with slightly
cooler...yet seasonable...weather then forecast to return over the
upcoming weekend. Ahead of this front...however...expect
oppressive heat to continue across the local area through the
afternoon hours Friday as temperatures once again climb to near
100 degrees and heat index values soar to between 102 and 108 by
the afternoon. With some elevated instability as well as forcing
from an associated short wave...expect this spell of heat to come
to an end as a better chance for thunderstorms returns to the
local area Friday night. While severe weather parameters are a
bit questionable...much of south central Nebraska is highlighted
for a marginal risk of severe weather Friday
evening/overnight...so kept a mention of this possibility in the
HWO. With this front slow to push south across the area...expect
a continued chance of thunderstorm into Saturday...with additional
small chances for thunderstorms expected off and on again through
the extended periods.
While this is not by any means a wet pattern...there will likely
be thunderstorms around at times with a return to more seasonable
temperatures for late July.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Thursday)
Issued at 724 PM CDT Wed Jul 19 2017
Will officially advertise a fairly "quiet" period with no formal
mention of thunderstorms and VFR ceiling/visibility, with the main
concern being a round of at least marginally-mentionable low level
wind shear (LLWS) overnight. However, there may be a few caveats
to consider, and these are mentioned in element-specific details
below.
Ceiling/visibility:
While confidence is rather high in VFR ceiling, the very high
surface dewpoints/humidity levels to bring into question the
possibility of at least light fog development. However, with
models even less favorable than last night for limited fog
formation (likely given greater boundary layer mixing), will keep
it VFR for now.
Thunderstorm potential:
While pretty much all models keep any legit thunderstorm potential
at least 50 miles north of both terminals through the period,
there is ongoing activity within 100 miles to the north, and there
are hints of at least weak convection skirting the area during the
day Thursday. Therefore, while not nearly enough evidence exists
to formally mention a thunderstorm, the chance is probably not
truly zero.
Winds (including LLWS):
Not accounting for any possible convective outflow effects,
surface winds will average from the south tonight and become more
southeasterly during the day Thursday (especially afternoon).
Sustained speeds the majority of the time should average under
12kt, but especially right away this evening some gusts closer to
20kt are possible. As a southwesterly low level jet ramps up this
evening/overnight (accelerating to 40-45kt within roughly the
lowest 1,000 ft.), this will set up a period of low level wind
shear advertised from 04z-12z.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Excessive Heat Warning until 8 PM CDT Friday for NEZ064-076-077-
085>087.
Heat Advisory until 8 PM CDT Friday for NEZ039>041-046>049-
060>063-072>075-082>084.
KS...Excessive Heat Warning until 8 PM CDT Friday for KSZ006-007-018-
019.
Heat Advisory until 8 PM CDT Friday for KSZ005-017.
&&
$$
UPDATE...Pfannkuch
SHORT TERM...Rossi
LONG TERM...Rossi
AVIATION...Pfannkuch
Area Forecast Discussion
National Weather Service Grand Rapids MI
814 PM EDT Wed Jul 19 2017
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 330 PM EDT Wed Jul 19 2017
A large complex of thunderstorms will move in during the early to
mid morning hours Thursday and bring potential for heavy rain
frequent lightning and some damaging wind gusts. It will remain very
warm and humid Thursday through Sunday with potential for several
more rounds of thunderstorms mainly from Friday night through
Saturday night.
&&
.UPDATE...
Issued at 814 PM EDT Wed Jul 19 2017
The high resolution models continue to indicate a second area of
thunderstorms will develop over central Wisconsin behind the first
storm complex currently diving southeast across west central and
southwest Wisconsin. The second area of storms will reach our
forecast area after about 4 am and may have gusty winds and
locally heavy rain. As a result I updated the current zone package
to reflect that idea.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 330 PM EDT Wed Jul 19 2017
Primary short term fcst concerns continue to involve determining
convective/svr wx/hvy rain potential through Friday night.
Active wx will develop early Thursday morning as an mcs rolls in
from the wnw. The mcs will develop over the upper midwest
(southern MN/WI) this evening on the nose of a strong llj. The
850-300 mb thickness pattern for MCS steering/propogation suggests
this mcs will move ese to se into our area during the early
morning hours Thursday.
In addition to frequent lightning and heavy rainfall there is
potential for the MCS to bring damaging wind gusts to portions of
our fcst area as strong 0-3km and deep layer shear is noted and the
MCS will probably evolve into one or several bowing segments. This
is the most likely scenario for our fcst area.
Though not the most likely scenario I am concerned about an outside
chance for a progressive derecho to develop over the upper midwest.
This could occur with mid/upper level winds parallel to the
stationary frontal boundary and sref guidance indicating the derecho
composite parameter will become very favorable over the upper
midwest late this evening. This notion is supported by progressive
derecho climatology and building heat over the central/eastern CONUS
as well.
A meso-high will begin to build in Thursday afternoon after the
MCS moves through which in conjunction with some lingering clouds
and a worked over atmosphere will result in minimal convective
potential for most of the aftn.
A consensus of short range guidance suggests that some instability
may develop by late aftn/early evening over our far southern fcst
area near the I-94 corridor where convection may redevelop. However
it seems the greater threat for convective redevelopment on old mcs
outflow boundaries will occur mainly just south of our fcst area.
Subsidence under a weak high pressure ridge should inhibit
convective development from Friday morning through most of the
afternoon. However a consensus of most of our latest short to
medium range guidance suggests convection will redevelop Friday
night to the north of a quasi stationary frontal boundary that
will be draped across northern IL/IN/OH by then.
This looks like a potentially very favorable setup for heavy rain
across portions of our fcst area as precipitable water values surge
to around 2-2.25 inches by 12Z Saturday. 1000-850 mb moisture
transport becomes increasingly favorable overnight. Some strong to
severe storms are also possible as elevated instability begins to
ramp up with favorable deep layer shear values of 35-45 kts.
As for late this afternoon... a few showers and perhaps a weak
isolated thunderstorm will continue to develop from near KAZO east
along the I-94 corridor.
.LONG TERM...(Saturday through Wednesday)
Issued at 330 PM EDT Wed Jul 19 2017
Wet and unsettled weather is expected to continue through Monday
with much drier conditions Tuesday and Wednesday. The main concerns
are thunderstorms with heavy rain on Saturday (possibly carried over
from Friday night) and the prospects for resultant flooding.
There are notable signals for heavy rain on Saturday. Several of the
last GEFS runs show QPF in the 95th percentile relative to its own
model climatology (also referred to as M-climate). This in theory
should account for the known wet and under-dispersive biases
associated with this particular ensemble. Even with this correction,
there remains a quite anomalous wet signal that has been apparent
for the last several runs. The NAEFS supports this possibility by
advertising very strong zonal flow in the lower troposphere and
seasonably high PWATs during this time.
Conditions will remain unsettled, but likely less organized, late
Saturday into Monday with a slowly approaching upper trough. As
noted before, seasonably cool and dry conditions are expected Monday
night into Wednesday as ridging at the surface and aloft build in
behind the exiting trough.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 741 PM EDT Wed Jul 19 2017
I expect a line of strong thunderstorms to pass through all of the
TAF sites between 09z and 15z (Northwest to Southeast). I used the
average of the latest ESRL HRRR (19z) and RAP model to come up
with the timing and also used it to get wind speeds and
directions. The timing of the storms may be off by as much as an
hour but I wrote it this way to you would have an idea how strong
these storms will be. I am not sure if they will be little sooner
or a little later but I am fairly confident there will be
storms that will have gusty shifting winds and very heavy rain,
followed by 2 to 3 hours from the stratiform rain area behind the
main line of storms. Skies should clear by early afternoon.
&&
.MARINE...
Issued at 330 PM EDT Wed Jul 19 2017
Fairly minimal wind and wave action is anticipated late this
afternoon through Thursday. The exception to this is during the
early to mid morning hours Thursday when a strong low level jet
will result in a bump up to southwest winds of 15 to 25 mph and
waves to 2 to 4 feet.
In addition a large thunderstorm complex will bring potential for
strong gusty winds and briefly higher waves during the early to
mid morning hours Thursday.
&&
.HYDROLOGY...
Issued at 330 PM EDT Tue Jul 18 2017
Although locally heavy rain is likely with thunderstorms moving
through the region into Thursday morning, the progressive nature of
the storms will limit the flood potential. What these storms may do
is set the stage (via antecedent conditions) for a possibly bigger
hydrologic event Friday night into Saturday. It is possible that PW
values will be near the maximum July values that have been recorded
going back to the 1940s (reference: SPC sounding climatology page
for DTX). Those maximum values are in the 2.00"-2.25" range. GFS,
GEM, and ECMWF guidance are strongly indicating a large area of over
2.00" PW for southern and central Lower MI for approximately a 24
hour window from Friday night into late Saturday, with some
solutions indicating over 2.25". This would equate to high rainfall
rates within any convection and an increased flood potential, at
least on local scales.
In terms of river flood potential, the main stem rivers would need
quite a bit of rain to go above flood stage, based on some ensemble
QPF analysis for the next 72 hours. Smaller rivers and streams would
be more prone to reaching flood stage with this setup. Still,
depending on where the storms move, the larger basins could be at
risk for considerable rises and possible flooding at certain points.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&
$$
UPDATE...WDM
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...TJT
AVIATION...WDM
HYDROLOGY...Hoving
MARINE...Laurens
Area Forecast Discussion
National Weather Service Gray ME
1012 PM EDT Wed Jul 19 2017
.SYNOPSIS...
A weak cold front will cross the mountains tonight...bringing
with it scattered showers. The front is expected to stall over
the area Thursday...allowing for another warm day to its south.
Temperatures are forecast to climb to near 90 again across much
of southern New Hampshire and nearby western Maine. Another
round of showers and thunderstorms are possible Thursday evening
and overnight...but the best chances look to be across southern
New England and New York State. Temperatures look to warm a few
degrees more into the end of the week and weekend as westerly
flow takes over.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
1010 PM...Forecast in generally good shape. Have fine tuned pops
based on scattered SHRA over the ME foothills, mostly associated
with weak mid level frontal boundary. Sfc front hard to find
attm, and this showers are showing bases around 7-10K ft for the
most part. RAP doing a good job with these showers which should
ESE through about midnight to 06Z and diminish.
750 PM...A few tweaks to Pops/T/Td/SKY/Wind based on current
obs. Main issue is what deal with the coastal fog/stratus for
the overnight, as it was eroding fairly quickly from the south
on the vis sat images before sunset. Models agree with this
trend and at some point it should slow with loss of heating.
Certainly not expecting the widespread dense fog of last night,
but could see some patchy fog late along the coast, as well as
the inland valleys. Coastal areas from the eastern end of Casco
Bay thru Penobscot are likely to see the most prevalent fog
tonight. Also, lowered pops a bit away front the intl border,
where precip is light and falling from 10K ft plus deck. Along
the intl border, closer to some forcing aloft, could see a few
sct convective cells, and maybe even a few rumbles of thunder
through around midnight or so.
Previously...A weak cold front is approaching the forecast area
from the NW...with scattered to isolated showers along it.
While an isolated rumble of thunder is not out of the
question...decreasing moisture and weak lapse rates aloft will
most likely preclude a widespread thunder threat. The front will
tend to get strung out along the forecast area tonight...with
showers gradually weakening towards morning.
Ahead of the front we will also likely see some areas of
fog/stratus move back into coastal areas N of PWM. Latest hi-res
guidance is less aggressive with inland extent than last
night...so I have mainly kept the fog confined to coastal
zones. That being said...a delay in the front and drier dew
points may allow more widespread fog to develop. So at this time
no dense fog advisory is expected...but I will allow later
shifts to monitor trends.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
With cold front expected to be strung out across the forecast
area...S of it will see another warm day with temps pushing 90
degrees. N of it is expected to be near normal for this time of
year. With weak pressure gradient continuing...sea breezes may
try to push inland again and keep coastal communities a few
degrees cooler.
Attention Thu will mainly be on thunderstorm chances in the late
afternoon thru the overnight. Model forecasts are consistent in
intensifying ongoing convection across MN...and tracking that
into the Wrn Great Lakes. This MCS is forecast to continue thru
the Lakes overnight...and emerge across NY Thu. Convection is
forecast to once again intensify with daytime heating. The
question is how far N will this convection make it. Current
trends suggest a more ESE track and more glancing blow possibly
for Srn zones. I have increased PoP to high chance along the MA
border...but it is still carrying a bit more uncertainty than
usual. A slight error in modeled placement of convection could
mean large changes in forecast across our area Thu/Thu night. It
does look like diurnal timing of storms will be unfavorable for
strong to severe storms to make it into the forecast area.
However an area of thunderstorms and locally heavy rain may be
possible across Srn NH if the more Nrn track verifies...like the
19.12z ECMWF shows. What rain does make it into the forecast
area will move E of the region by Fri morning.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
The models are in decent agreement on the long wave pattern
through early next week. Thereafter, big differences emerge
regarding the degree of residual troffiness here in New
England. Overall, we`re likely to see both heights and
temperatures run below average for much of the extended period.
We begin the period with a westerly flow and a broad low
amplitude trough here in New England. Weak ridging arrives by
Sunday in response to digging upstream shortwave energy over the
Great Lakes. By the start of the new work week, this energy has
carved out a sizable trough across the Great Lakes and
northeast CONUS. The trough axis will inch eastward across the
region through the remainder of the forecast period. In the
dailies...we begin the period with a cold front across southern
New England...and a second cold front approaching the
international border from the Saint Lawrence Valley. This
boundary will drop south across the forecast area on Friday with
widely scattered convection. The third and final cold front
will drop south across the region Friday night and Saturday with
scattered convection. By early Sunday, the boundary will be
stalled across southern New England with weak ridging providing
a decent day across for Northern New Hampshire into much of
Maine. Southern New Hampshire into extreme southwest Maine will
be closer to the stalled boundary and associated cloud shield
with onshore flow potentially adding some low clouds and fog to
the mix. By Sunday night...the frontal zone will ride back north
with attendant cloud shield as well as increasing pops and cool
unsettled weather in response to evolving upper trough.
&&
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Short Term...Areas of fog are expected to form again tonight N
of PWM. Most likely RKD sees IFR or lower conditions for a good
portion of the night...though AUG may see some lower CIGs sneak
into the area after midnight. Otherwise isolated SHRA are
possible tonight from HIE and LEB early this evening through AUG
and RKD after midnight. On Thu an area of SHRA/TSRA will move
thru the Northeast on an ESE trajectory. The bulk of this looks
to miss the forecast area...though it is possible a more Nrn
track will bring SHRA/TSRA to MHT/CON/PSM in the evening.
Confidence is low in that outcome however.
Long Term...
Fri...Isold MVFR psb in -shra/-tsra.
Sat...Sct MVFR in -shra/-tsra.
Sun night - Mon...areas of MVFR in -shra/-tsra with lcl IFR in
coastal stratus and fog.
&&
.MARINE...
Short Term...Winds and seas are expected to remain below SCA
thresholds. Marine fog/stratus are expected to form again
tonight N of Cape Elizabeth. The fog is gradually expected to
dissipate as a weak cold front approaches early Thu morning.
Long Term...
Sat PM - Sun AM...Winds and seas could briefly approach small
craft outside the bays.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.
&&
$$
SYNOPSIS...
NEAR TERM...Cempa/Legro
SHORT TERM...Legro
LONG TERM...Schwibs
AVIATION...Legro/Schwibs
MARINE...Legro/Schwibs
Area Forecast Discussion
National Weather Service Wilmington NC
1020 PM EDT Wed Jul 19 2017
.SYNOPSIS...
Showers and thunderstorms will be isolated in the days ahead,
as an upper ridge builds from the west. The ridge will bring hot
and humid conditions through the weekend. Rain chances may
increase early next week, as a surface trough deepens inland.
&&
.NEAR TERM /THROUGH THURSDAY/...
As of 1000 PM Wednesday...Afternoon thunderstorms dissipated
quickly early this eve and the remaining showers have since
faded as well. A mid/upper level trough remains across the
eastern Carolinas with the low center positioned along the South
Carolina coast. In this environment it is always difficult to
completely remove POPs, but we feel confident cool and
stabilizing outflow has largely worked through the Forecast
Area. The high resolution HRRR does not indicate any showers
redeveloping across the area overnight. However, given what
transpired this morning and with the NAM and GFS showing early
morning redevelopment near the Cape Fear area, we do show POPs
increasing to slight chance along portions of the coast around
and just after sunrise.
Fog and stratus should fill in for a time given the wet ground
and light flow across the area and have included patchy fog
around and shortly after daybreak/sunrise. Lows were notched
down as again cool thunderstorm outflow has worked across the
area, so mainly lower 70s with mid 70s at the beaches.
Guidance brings isolated convection mainly to our coastal
counties for Thu. A warming trend commences with highs in the
lower to mid 90s and heat index values of around 100F.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 300 PM Wednesday...Two upper ridges, one centered over the
western Atlantic and the other over MO "reconnect" Thursday night as
upper low retrogrades south and west into JAX. At the surface the
gradient will be quite weak as we sit between two areas of high
pressure. The area will be rain-free but some fog is tough to rule
out. Friday into Friday night the upper low continues to retrograde
and weaken allowing the two ridges to further connect to our north
while a surface piedmont trough takes shape. Though the latter and
the healthy seabreeze will both try to serve as foci for
thunderstorm development it looks too dry with midday forecast
soundings showing dewpoint depressions of 25C not uncommon at some
levels above the boundary layer. Rain-free conditions will persist
into Friday night and once again some areas of fog seem possible due
to the weakness of the piedmont trough keeping winds light.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 300 PM Wednesday...The first half of the extended period,
basically the weekend will feature mostly dry conditions with
temperatures somewhat above normal. These conditions will be
provided by a weak mid level pattern and Bermuda High Pressure
at the surface. The mid level capping is not quite as prominent
on soundings as it has been in recent days, but with mid level
moisture lacking convection will still drive a hard bargain. The
second half of the extended, early next week shows more
favorable conditions for convection as cooling aloft and an
increase in column moisture to well over two inches warrants.
Temperatures fall slightly from the weekend`s warmer readings.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
As of 00Z...Isolated showers will dissipate through midnight.
Stratus and fog are expected to be develop between 08-12z and
did include IFR at most of the terminals during this time.
Otherwise, prior to 08z and after 12z, VFR is expected. However,
with the lingering impacts of the upper trough, can not rule
out showers and thunderstorms on Thu and possibly as early as
Thu morning. Showers should be isolated to widely scattered.
The probability of convection moving across a terminal to
produce flight restrictions is too low for inclusion in any of
the TAFs at this time.
Extended Outlook...VFR except for brief periods of lowered cigs
and vsbys in isolated convection through Monday.
&&
.MARINE...
NEAR TERM /THROUGH THURSDAY/...
As of 1000 PM Wednesday...A weak pressure gradient will prevail
through Thu. The waters will continue to be under the influence
of a mid and upper level trough. A land breeze will shift light winds
to a more W or NW direction overnight. SSW to SW winds will return
during Thu and increase to 10 to 15 kt during the afternoon.
Seas will be 2 to 3 ft and largely a function of an ESE swell
with a period of 7 to 9 seconds.
SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 300 PM Wednesday...Conditions generally unchanging through the
period and they will be typical of the time of year. Wind will be
out of the southwest due to Atlantic high pressure and a piedmont
trough will struggle to develop late in the period. Spectral wave
bulletins suggest that a 10 second SE swell becomes more pronounced
than the 4 second wind chop for a general forecast of 3 ft seas.
LONG TERM /SATURDAY THROUGH MONDAY/...
As of 300 PM Wednesday...Bermuda High Pressure will maintain a summertime
flow across the waters. Mariners can expect a southwest flow of 10-
15 knots with some late morning/afternoon acceleration with the sea
breeze near shore. Significant seas, without the assist from any
meaningful swell component will fall into a range of 2-4 and mostly
2-3 feet.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.
&&
$$
NEAR TERM...RJD
SHORT TERM...MBB
LONG TERM...SHK
AVIATION...RJD
Area Forecast Discussion
National Weather Service Lincoln IL
900 PM CDT Wed Jul 19 2017
.UPDATE...
Issued at 900 PM CDT Wed Jul 19 2017
Current forecast for most of CWA looks fine. However, will need to
be making some adjustments in the north part of CWA where its
closest to the bow echo moving through northeast IL. Radar
indicates that outflow from storms is pushing out ahead of storms
that were to the south/back of the main push. So would only expect
scattered to isolated stuff in north and northeast parts of CWA.
HiRes models still indicate another MCS later tonight moving
through northern/northeast IL...so will keep pops going in the
north overnight as well. Update should be out shortly.
&&
.SHORT TERM...(This evening through Thursday)
ISSUED AT 306 PM CDT Wed Jul 19 2017
High-res visible satellite imagery is showing an enhanced Cu field
along the I-80 corridor and east of I-55 this afternoon. Isolated
thunderstorms will develop across these areas over the next couple
of hours...as per the ARW/NMM/HRRR. Any convection that fires will
rapidly dissipate by sunset, leaving behind mostly clear and dry
conditions early this evening. The next short-term forecast
concern will be the track/timing of a cluster of thunderstorms
currently ongoing over southwest Minnesota. These storms initiated
over the western Dakotas this morning and have been tracking
southeastward throughout the day. Think they will continue in this
general E/SE direction along a stationary frontal boundary through
the evening hours. Most recent runs of the HRRR show the cluster
entering north-central Illinois later this evening, brushing the
far northern KILX CWA after 03z/10pm. Have therefore updated
PoPs to include low chances along/north of I-74 tonight. While
this initial round of storms will diminish as it drops
southeastward into the area, a larger MCS will likely take shape
further north across Minnesota into Wisconsin. These storms will
also track E/SE, but will remain north of central Illinois later
tonight into Thursday morning. Will continue to carry slight
chance PoPs along/north of I-74 into Thursday morning, but think
the system will stay north of the CWA. Once the morning MCS drops
into northern Indiana, another hot and humid day will unfold
across the region. High temperatures will rise into the lower to
middle 90s, while heat index readings reach the 105-110 degree
range. The morning convective complex will push the synoptic
frontal boundary further south, with most models showing it along
or just south of I-80 by Thursday afternoon. With a boundary in
the vicinity, decided to carry slight chance PoPs across the N/NE
Thursday afternoon.
.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 306 PM CDT Wed Jul 19 2017
An active weather pattern will persist through the end of the
week, with several nocturnal storm complexes expected to develop
and ride along a stationary frontal boundary draped across
northern Illinois. Hot and humid weather will prevail across the
KILX CWA, with afternoon highs climbing into the middle and
perhaps upper 90s Thursday through Saturday. With dewpoints
remaining in the 70s, peak afternoon heat index values will reach
105-110 degrees...prompting the continuance of heat headlines
across the entire area through Saturday evening. Storm chances
will generally be confined to the north through the period, as
strongest forcing will remain across northern Illinois.
A significant short-wave will push the frontal boundary southward
by Saturday, setting the stage for a round of showers and
thunderstorms across central Illinois. With strong instability as
characterized by both NAM and GFS CAPE values in excess of
4000J/kg, strong thunderstorms with torrential downpours will be
likely. Main mitigating factor for widespread severe weather will
be weak wind-shear, with most models suggesting the strongest
shear will lag well to the north of the primary instability axis.
Nevertheless, think thunderstorms are a good bet Saturday
afternoon and evening.
The cold front will drop southward into the Ohio River Valley by
late Sunday, triggering a few additional storms across the
southern half of the CWA Sunday afternoon. After that, a
cooler/drier airmass will settle into the region for early next
week...with high temperatures dropping into the lower to middle
80s by next Monday and Tuesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 631 PM CDT Wed Jul 19 2017
Expecting skies to be clear most of the evening at all TAF sites.
However, a line of convection occurring in northeast IA, headed
for northwest and northern IL has the potential of sliding more
southeast than currently and could bring some thunderstorms to the
northern three TAF sites later tonight. Will have VCTS at PIA/BMI
and CMI tonight and lasting about 4hrs at each site. Beyond this,
high cirrus is expected remainder of the overnight hours and
through tomorrow. Winds will be light and variable tonight, but
then become southwest tomorrow at less than 10kts.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
Excessive Heat Warning until 8 PM CDT Saturday for ILZ027>029-
036-037-040>042-047>054-061-062-066>068-071>073.
Heat Advisory until 8 PM CDT Saturday for ILZ030-031-038-043>046-
055>057-063.
&&
$$
UPDATE...Auten
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Auten
Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
643 PM CDT Wed Jul 19 2017
.UPDATE...
Issued at 453 PM CDT Wed Jul 19 2017
Updated forecast for severe thunderstorm watch
&&
.SHORT TERM...(This evening through Thursday)
Issued at 311 PM CDT Wed Jul 19 2017
The model blend of HRRR, HRRR exp and RAP are close to the synoptic
NAM and GFS. Weakly organized MCS activity is expected this evening
across Nrn Neb which could last into Thursday morning. 500 mb winds
aloft remain weak at 25 kt or less but moisture is robust with
ambient precipitable water north of 1.5 inches. The models suggest
just an isolated heavy rain potential with the storms tonight.
The forcing is off the Black Hills and associated with a southward
propagating cold front. POPs for this forecast are limit at 30
percent. Our friendly RAP model continues to show very warm
temperatures near 15C at 700mb which could represent significant
inhibition for storm development.
The temperature forecast uses blended bias corrected guidance for
lows in the upper 60s to lower 70s tonight and blended guidance plus
bias correction Thursday for highs in the upper 80s to lower 90s
north. Upper 90s to around 100 are expected south and a heat
advisory may be necessary across Chase, Hayes and Frontier Counties.
The NAM, GFS, GEM and SREF blend suggest additional MCS activity
north of the stationary Thursday afternoon across Nrn Neb. Winds
aloft are still weak, less than 25kt in the NAM and GFS, and there
are timing differences. The GFS is about 6 hrs faster than the NAM
which holds off on the MCS until Thursday evening.
.LONG TERM...(Thursday night through Wednesday)
Issued at 311 PM CDT Wed Jul 19 2017
The models show MCS activity growing upscale across Nrn Neb Thursday
evening. The outflow from these thunderstorms should sweep south and
cool down Swrn Neb Friday. Bias corrected model data from the NAM,
GFS, ECM and GEM models still forecast highs well into the 90s to
around 100 Friday so their is a dispute in the forecast as to how
warm it will be. Despite the outflow, h700mb temperatures in the
models appear to rebound to the 16-17C range which is very warm.
All models cool temperatures Saturday as the h500mb ridge moves into
the midsouth. The upper level ridge remains south Sunday and builds
west into the desert Southwest. This sets up northwest flow aloft
with cooler Pacific and Canadian air moving into Nebraska Sunday
through Wednesday.
The rain forecast is less predictable. The cooler temperatures aloft
and northwest flow will support thunderstorm development off of the
Black Hills and Big Horns. Scattered rain chances are in place
Friday and Saturday associated with a cold front drifting south
through the Central Plains. Moisture becomes limited Sunday and
beyond for generally isolated chances of showers and
thunderstorms.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 640 PM CDT Wed Jul 19 2017
Thunderstorms will continue along a line from KSNY to just south
of KVTN to KONL through the late evening. Storms in the vcnty of
KONL are severe with 60mph or greater winds and hail to the size
of ping pong balls. Winds to the north of this line are shifting
to the north and continue out of the south to southeast to the
south of the line. Clouds will move into western Nebraska from the
west overnight with cigs AOA BKN120.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT /7 PM MDT/ this evening for
NEZ005>010-022>029-035>038-056>059-069>071-094.
Heat Advisory from 1 PM CDT /noon MDT/ to 8 PM CDT /7 PM MDT/
Thursday for NEZ038-069>071.
&&
$$
UPDATE...Power
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Power
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
1019 PM CDT Wed Jul 19 2017
.MESOSCALE DISCUSSION...
1010 PM CDT
The convective line continues to very slight weaken as it heads
into northwest Indiana. Gusts of 45-55 mph were observed across
Will County including here at the WFO (53 mph). Base velocity
values on the KLOT radar do indicate some pockets near 60 mph,
however that has been as the storms have been moving away and the
radar vantage point is more elevated. The environment indicates a
little more MLCIN into far northwest Indiana, however given the
very moist low-levels, it likely will continue having 40+ mph
winds across Kankakee County (44 mph at IKK recently) and
northwest Indiana. Even further south toward Ford and Iroquois
Counties, outflow ahead of the storms looks to be producing 35-45
mph gusts.
Further north, underneath the MCV/broad bookend vortex, there have
been 40-50 mph non-thunderstorm gusts and sharp pressure rises in
far southern Wisconsin. While this MCV will drop south-southeast
into northern Illinois, it is uncertain on how far southeast these
winds will advance. The long-lived nature of this complex would
point toward at least some inroads of these winds into far
northern Illinois. It will be something to watch, especially in
areas that sustained wind damage from the earlier storms.
MTF
&&
.SHORT TERM...
319 PM CDT
Through Thursday...
For the remainder of the afternoon into early evening, the main
concern will be isolated shra/tsra developing ahead of a lake breeze
pushing inland. Latest vis satellite shows the lake shadow of clear
air moving inland with sct cu/tcu/shra/tsra developing in the
undisturbed warm/moist/unstable environment. Without a significant
organizing trigger, other than the lake breeze boundary itself,
activity should remain isold/widely scattered. There should be no
severe threat from any tstms that develop, there will be the
potential for locally heavy rainfall as pwats are around 2 inches
over the area. This activity should largely be diurnal and
dissipate with sunset. For the overnight hours, thunder concerns
will shift to a developing MCS moving through srn MN this afternoon.
The models have been all over the place with this system, both the
CAMs and the larger scale models. The latest GFS seems to have the
better handle on this system and the short term wx/pop/qpf forecast
has trended closer to this solution than the NAM, especially, which
has been a more northern track outlier. The general trend is for
the MCS to track along an instability corridor, through nern IA/swrn
WI and into nwrn IL by arnd midnight. Timing is still a bit
uncertain and will depend on how the system develops upscale, but
latest thinking is that any thunder will hold off until arnd
midnight for the Rockford area and then spread southeast into the
Chicago metro area drug the early morning hours. There has been
some suggestion in the guidance that some secondary development may
occur in a warm advection zone following the passage of the main
MCS. This could allow some ts to linger into the morning hours
tomorrow. There will be some severe threat with the main MCS, with
the primary threat being strong damaging wind. Locally heavy
rainfall will also be likely, which could aggravate the ongoing
flooding issues on the Des Plaines and Fox Rivers. Expect that the
system will be relatively progressive, so any heavy rainfall should
be transitory and not sit in one location.
For Thursday, increasing heat and humidity will become a concern in
addition to renewed thunderstorm chances in the afternoon. The
trend for tomorrow and into the extended forecast period will be for
unsettles weather and periods of thunderstorms with periods of
locally heavy rainfall possible. As for heat and humidity, expect
that temperatures across much of the area should reach into the low
90s with dewpoints in the low to middle 70s. The highest temps and
dewpoints should be confined to locations south of the I-80
corridor. Heat Index values may reach 105-107 F tomorrow south of I-
80 and a heat advisory may be required. have trended a bit higher
than guidance on the temps and dewpoints, given the general synoptic
pattern, so will hold off on issuing a heat advisory at this time and
see how conditions evolve. Thunderstorm chances should be low
tomorrow with mid level warm advection keeping some capping, but
will maintain a corridor of low chance to slight chance pops for
tsra along the main corridor of sfc instability.
&&
.LONG TERM...
306 PM CDT
Thursday night through Wednesday...
Biggest concern in the extended is convection that may lead to heavy
rain Friday and Friday night. Chances of storms continue through the
weekend before a dry period sets up for the first half of next week.
Expecting daytime convection to continue into Thursday evening/night
ahead of the cold front. The cold front will stall over the far
southern portion of the forecast area. Additional convection is
expected Friday. There will be two areas of focus: the stationary
front south of I-80 and an upper level disturbance shifting
northeast from Iowa into southern WI. The GFS suggests PWAT values
will be 2-2.25 inches, which is well above climatology and near the
upper end of daily maxima for mid to late July. Mid level flow is
around 40 MPH so while storms should be moving at a decent pace,
heavy downpours are likely.
The GFS appears to be capturing the current situation the best so
weighed the forecast in its direction. While thunderstorms are
possible across the forecast area Friday afternoon, think the best
chance will be south of a Rockford to Valparaiso line. However,
convection will spread to include all of the forecast area in the
evening, and an organized convective complex will likely shift
southeast through the region Friday night. This complex will lead to
additional heavy rain that parts of the area do not need. Will
continue to highlight our thoughts about heavy rain in an ESF and
the hydrology section below.
Flow off the lake will likely keep temps along the lake in the 80s
while the rest of the region will be in the mid 80s to around 90.
Dewpoints in the 70s will lead to heat indices from 90-100 north
of I-80 to 100-106 south of I-80.
I have medium confidence in Saturday`s forecast as the convective
complex should still be overhead Saturday morning. Convection should
work over the atmosphere, and I am unsure how quickly we will be
able to recover Saturday afternoon. If we can recover, thinking the
best chance for additional storms will be along and east of I-55.
The hot, sticky conditions continue Saturday with highs in the mid
80s to the low 90s and heat indices in the mid 90s to up to 106
degrees.
Cooler and drier air arrives Sunday with highs in the 80s. High
pressure slowly shifts east and reaches Lake Michigan Tuesday
afternoon. I have dry conditions in the forecast through at least
Tuesday night if not into Wednesday. Models are slowing the next
system mid week so Wednesday may be drier than currently forecast.
JEE
&&
.HYDROLOGY...
The Hydrologic Outlook (ESF) for along and north of I-88 has been
continued due to concerns of multiple rounds of storms through
early this weekend. Observational trends are supporting the
forecast in terms of a very moist atmosphere over the area from
now through Saturday, with pwats in excess of 2 inches. The
confidence on receiving a burst of heavy rain with a quick-moving
storm complex in far northern Illinois late tonight has increased,
but some uncertainty still resides in exact track of this system.
Where the center of it passes certainly will have potential for
1"-2" in around 1-2 hours.Typically, with such quick moving
storms, even if intense, the tendency is to produce widespread
averages more of 0.50"-1.00". If there were to be some slower
movement or backbulding, concerns would raise for renewed
flooding.
Wet antecedent conditions particularly over the Des Plaines and
Fox River basins provide concerns through the rest of the week as
storm chances increase Thursday night and into Friday. Location
of this rainfall is even more uncertain, however there may be
higher concern of additional flooding given it is a regime that
could favor training storms and very efficient rain-producing
storms.
MTF/ASK
&&
.AVIATION...
For the 00Z TAFs...
Some significant changes to the near term TAF due to the ongoing
MCS nearing northwest IL that has a history of strong winds. HRRR
model the only one grasping onto it and it is still a few hours
too slow. The MCS should continue to propogate southeastward
toward the terminals this evening. Expect strong northwest winds
behind the MCS, gusting to 60 mph or higher at RFD and points west
of the lake breeze axis. A bit more uncertainty with the severe
potential closer to ORD/MDW, but do feel there will be a period of
storms and gusty northwest winds to the terminals as well.
Did not make any significant changes beyond the near term, there
does appear a decent signal that another round of storms will form
across MN overnight and move southeastward again into the area
late tonight into early Thursday. Confidence on specific timing
and impacts is low, but will reassess with the 3z AMD once we get
through round 1.
We did leave the Prob30 tomorrow afternoon, but some concerns
about the trigger and coverage. There could be a northeast wind
shift to help as a trigger for convergence with subtle waves in
the upper level flow. Low confidence on the NE wind shift at ORD
tomorrow, but do feel there will be a NE wind shift at some point
tomorrow afternoon/early evening.
KMD
&&
.MARINE...
306 PM CDT
Looking at a relatively quiet period over the lake through next
week. Weak high pressure currently over the lake will continue east
tonight. Winds become southerly behind the high early Thursday
morning and then continue to veer through the day. The baggy
pressure gradient will likely result in periods of variable wind
directions across the lake.
Another weak high moves over the lake Friday morning. Winds become
southeast by the evening, and speeds may increase to 15-25 kt over
the southern end of the lake. Guidance indicates the gradient may
increase over the southern end of the lake Friday evening, but do
not have a lot of confidence in the pattern.
Low pressure passes over the lake this weekend with westerly flow
becoming northerly across the lake by Monday morning. North winds may
reach 15-25 kt for a time Sunday afternoon into Monday. Northerly
flow stays over the lake until the high moves over the lake Tuesday
evening. Persistent northerly flow may result in waves hazardous to
small craft Sunday night into Monday.
JEE
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
559 PM CDT Wed Jul 19 2017
.UPDATE...For 00z Aviation discussion below
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.SHORT TERM...(This evening through Thursday)
Issued at 424 PM CDT Wed Jul 19 2017
Ongoing severe MCS will exit to the southeast quickly late this
afternoon. The forecast then becomes quite uncertain for this
evening and overnight with convective redevelopment possible
across central Minnesota. The atmosphere seems to be recovering
somewhat across South Dakota and there have been a few cells over
west central MN this afternoon. The HRRR would imply an east-west
line of storms developing between 02-03Z across central MN and
progress southeast for the rest of the evening into the early
overnight hours. This activity would contain a large hail threat,
although some damaging wind gusts are also possible. The biggest
threat will be heavy rainfall with training cells, but CAMs seem
to keep the line progressing southward which would limit flash
flooding potential.
.LONG TERM...(Thursday night through Wednesday)
Issued at 445 PM CDT Wed Jul 19 2017
For the extend, we`ll see our zonal flow transition over to
northwest flow this weekend, before going back more zonal by the
middle of next week. Most concerning period looks to Thursday night
into Friday, when another round of severe weather and heavy rainfall
looks possible.
Our dry weather Thursday will be short lived as moisture quickly
returns Thursday night from Nebraska toward southwest MN. Most of
the guidance is in agreement with an elevated band of thunderstorms
working into southwest MN. This will push the warm front back into
southern MN Friday afternoon, and guidance is in good agreement on
storms firing off along this front and heading southeast toward
Chicago Friday night. Some discrepancies with how far north this,
but we followed the more southern solutions for QPF Friday, like the
GFS for Friday as what are seeing today has tracked south of even
what the southern models had. Moisture, instability, and shear
parameters all look similar to what we are seeing today, so all
modes of severe weather will be possible, but upscale growth to an
MCS looks likely, probably tracking from south central MN over
toward southern lower Michigan.
For the weekend, it is looking up weather wise, as a secondary
shortwave in the increasingly northwest low drops across northeast MN
toward the U.P. of Michigan, with the majority of activity Saturday
night into Sunday staying off to our northeast.
We`ll have dry weather to start next week, but by Tuesday, moisture
will be surging back north across the Plains, with thunderstorm
chances returning Tuesday night into Wednesday as a front works into
the area.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 600 PM CDT Wed Jul 19 2017
In the wake of the showers and storms there will be a period of
benign weather, but another round of storms may develop across
central MN/WI after 03z into the overnight hours. MVFR cigs/vsbys
would be possible attendant with the storms, including patchy fog
and MVFR cigs in the wake of the precip with the warm front
stretched across the area. After daybreak Thursday clear skies
will prevail with northwest winds of 7-10 knots.
KMSP...
The next round of storms looks to develop around 03z, and persist
through around 07z. MVFR cigs/vsbys will be possible during that
time, and cigs around 1500 feet may linger through the morning
push. After 14z clear skies and northwest winds around 8 knots
prevail.
/OUTLOOK FOR KMSP/
Fri...Mainly VFR. -SHRA/TSRA likely. Winds SE 5-10 kts.
Sat...Mainly VFR. Chc MVFR in -SHRA/TSRA. Winds lgt and vrbl.
Sun...VFR. Wind NW 10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&
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SHORT TERM...BORGHOFF
LONG TERM...MPG
AVIATION...LS