Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/21/17
Area Forecast Discussion
National Weather Service Buffalo NY
1015 PM EDT Wed Sep 20 2017
Warm temperatures and dry conditions will persist through the
remainder of the week and the coming weekend, as high pressure will
remain in place across the region.
.NEAR TERM /THROUGH THURSDAY/...
Skies have cleared out this evening outside of some high thin
clouds clipping Central New York and the Eastern Lake Ontario
region. The clear skies and light winds will set the stage for
another foggy night for many areas later tonight and into early
Thursday morning, particularly in river valleys and near
lakes/ponds. Similar to last night, fog and low stratus is
likely to develop along the south shores of Lake Ontario. This
cloud cover will linger into Thursday morning before dissipating
by Thursday afternoon.
With ideal conditions for radiational cooling and slightly
lower dewpoints, we should see cooler temperatures as compared
to Tuesday night, with lows in the 50s, with a few lower 60s
near Lake Erie.
Thursday will be another near carbon-copy of today with perhaps the
only differences being the mid-level ridge strengthening to 588dm
and 850mb temps warming a degree to +17C. The high pressure surface
and aloft will keep dry and warm weather in place with high temps
again warming into the low to mid 80s or 10-15 degrees above normal
September levels. Dewpoints holding in the 60s will keep a humid
feel to the airmass.
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
The calendar will remain turned back a couple months through this
period...as an anomalously strong 590dm sub tropical ridge will
remain anchored over the Ohio Valley and Lower Great Lakes. This
prodigious ridge will be accompanied by equally exceptional warmth.
H85 temps tat will start off in the mid teens C Thursday night will
further warm to the upper teens C for the weekend. This will
encourage additional day to day warming so that by Saturday...max
temps will be in the mid to upper 80s F. Given the increasingly dry
antecedent conditions...its not out of the question that select
locations in the Genesee Valley (ie. Dansville) and in the typically
warmer valleys of the Southern Tier would reach 90. If this were mid
summer (when the sun angle would be more than 20 deg greater) then
we would possible be talking about some oppressive heat. Luckily for
us...the Gulf of Mexico will be cut off..so dew points that will
start off in the upper 50s to lower 60s will not climb past 65 by
late in the weekend.
Meanwhile the nights will feature mainly clear skies with the
resulting favorable radiational cooling producing fog in open...
outlying areas...and particularly in the Southern Tier valleys. Mins
will range from the mid and upper 50s across the Southern Tier and
parts of the North Country to the low to mid 60s across the lake
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A very high confidence forecast remains in place for the
unseasonable warmth to continue during this three day period...as a
high amplitude ridge will remain intact across the eastern third of
the country. The only problem will be the possible effects from
Hurricane Maria...which by Wednesday will likely be churning
northward of the mid Atlantic coast. While the ridge will keep us
rain free through at least Tuesday...there have been some medium
range ensembles that are suggesting that some Atlantic moisture
could work back across the region late Tuesday night and Wednesday.
From this vantage point though...the odds favor continued dry
weather...but will introduce slgt chc pops as we end the seven day
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
VFR conditions are in place late this evening, however these
will deteriorate as light winds and clear skies promotes the
development of radiation fog. Tonight should be somewhat
similar to last night, except that the northeasterly flow will
be stronger across the eastern half of Lake Ontario rather than
the western half. Stratus and fog is again likely to form along
the south shores of Lake Ontario. Following HRRR guidance which
had a good handle last night, this should be most widespread
from Rochester to Syracuse which is downwind of a NNE surface
flow. Fog will also form in the river valleys, impacting
Jamestown. Elsewhere fog will be patchy, but it is difficult to
rule out at any given location.
Visibility will vary in radiation fog, but there is a potential
for VLIFR conditions in dense fog at times. This has the
greatest chance to impact ROC/JHW, but cannot completely be
ruled out at any terminal location.
Stratus will linger south of Lake Ontario during the morning
hours Thursday, with lingering IFR conditions in low cigs. This
will dissipate by Thursday afternoon with VFR conditions.
Thursday night through Monday...VFR. Local IFR conditions each
late night and early morning with fog.
High pressure will remain in place across the Lower Great Lakes
right through next weekend. This will provide a long stretch of very
light winds and flat wave action for the rest of the week and
weekend with ideal boating conditions, but not much wind for sailing.
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1155 PM EDT Wed Sep 20 2017
Cirrus canopy from Wisconsin convection is expanding steadily east
into area. This should limit fog potential tonight and the current
forecast of MVFR to occasional IFR vsbys late seems reasonable. A
few showers may survive the trip into southern lower Michigan and
brush KMBS with some small chance of formation later in the day on
boundary left along northern fringe of upper ridge. There is still a
hint or two that at least a scattered deck in the 3-5kft range will
try to formation late tonight (coinciding with best time for BR) on
nose of higher theta-e air working into area.
For DTW...Period of patchy fog on the edge of MVFR/IFR possible by
late tonight/early Thursday morning with perhaps a period of sct or
bkn 3500-4500 foot clouds as deeper moisture also works back east
//DTW THRESHOLD PROBABILITIES...
* Low for ceilings aob 5kft late tonight, ~09z-13z.
Issued at 409 PM EDT Wed Sep 20 2017
Most important item to communicate is long stretch of summerlike
warmth and humidity that will begin tomorrow and run through Monday.
High confidence exists in daytime temperatures running in the middle
to upper 80s with dewpoints in the 60s to near 70.
With negative PNA in place, the central Great Lakes will remain
nestled right along the interface between equally large wavelength
eastern Conus ridging and deep PAC NW and Western Canada PV
reservoir. The peculiar aspect of this particular setup, and what
provides a reasonable amount of uncertainty during the next 24 to 36
hours, is that while the upper level ridge will begin to reamplify
aggressively in response to at least partially all of the tropic
activity offshore, the ridge itself is one that does not have an
overwhelming amount of support for downward vertical motion below
500 mb. Rather, much of the model data suggests that pesky low
shower and thunderstorm chances Thursday and Thursday night will
hinge upon the ability of pre-existing convective shortwave energy
to survive downstream off of Rossby wave breaking.
This afternoon and tonight. NWP matches up well with most recent
Water Vapor imagery in showing corridor of deep drying associated
with strong anticyclonic vorticity that is now pushing into
southeastern Michigan this afternoon. Associated subsidence bubble
in the 3.0 to 9.0 kft agl layer has been very efficient in eroding
low cloud today. All that remains is a bkn boundary layer cumulus
that resides in much of the eastern cwa. Some congestus exists in
the lake convergence axis along the Lake Huron shoreline. So while a
sprinkle or brief shower will be possible in the eastern Thumb this
afternoon, there is very little signal to support anything more than
that. Regarding fog potential tonight. Plan view perspective of
forecasted theta e fields strongly supports that higher lower
tropospheric moisture content that had been in place last night as
been squeezed out of the cwa to the east. Surface pressure
condensation pressure deficits out of the HRRR suggests that best
potential for fog will exist within this air mass over southwestern
Ontario. There is some signal that suggests fog could bleed back
westward around daybreak and impact portions of the eastern thumb
down into Macomb County. Otherwise, additional drying from the
subsidence mentioned above should limit formation. Time of year and
warmer dewpoints still supports carrying a patchy fog mention for
shallow radiational fog potential.
Thursday. Interesting forecast with alot of moving parts. First
thing will be watching for is the relatively strong elevated mixed
layer plume that will fold over from Wisconsin/Northern Plains today
into southeastern Lower Michigan Thursday. This folding over of the
higher theta e ridge will be caused by incredibly strong 1000-500mb
geopotential height rises occuring over the upper Mississippi River
Valley and Western Lake Superior tonight. The increasing lower
column high pressure, complete with a mesohigh, and rapid change to
anticyclonic curvature will shove the warm and humid air into the
region. Model data continues to support some convective shortwave
energy and pre-existing shower and thunderstorm activity surviving
within the EML across northern Lower Michigan and pushing into the
Saginaw Bay after daybreak. With the strong ridging, only be looking
at remnant elevated thunderstorm activity above 8-10 kft agl layer.
Overall, just looking at some shallow isentropic lift wash with no
upper level jet support, no low level jet. Confidence in showers and
thunderstorm during the morning across the north is low.
The second item to watch for will be exactly where the exact edge of
an internal surface ridge structure develops. Model guidance
suggests the main axis will develop to the east of the cwa with at
least a part of the western edge back into the area. This local
maximum to the ridge appears to set up directly under the corridor
of the strong anticyclonic vorticity that was discussed earlier. The
importance of this ridge is twofold as it will directly impact to
what degree temperatures will reach Thursday, but also set a hard
edge to the capping of any thunderstorm chances. Definitely will be
very warm and humid with temperatures pushing middle to upper 80s.
One certainly needs to stress the warmth as heat indices in many
areas will likely push to and exceed 90. Really dont think we will
see runaway highs in here in southeastern Michigan with such rich
moisture, some residual southeasterly flow trajectories, and lack of
mechanical mixing or southwesterlies.
Thunderstorm chance for Thursday is the tricky forecast. Models
including the ECMWF and regional GEM remain steadfast in keeping a
persistent scattered shower and potential thunderstorm chances in
play across the north particularly in and near Saginaw Bay. This
positioning is curious because this would be along the west edge of
the surface meso-ridge. The uncertainty is a result in the complete
lack of any synoptic scale lift. The eye-raising aspect of the
thermodynamic environment Thursday is the steep 800-600mb lapse
rates that will result in SBCAPES in the 2000-2250 J/KG range. There
will be a complete lack of shear with 0-6km bulk shear at less than
10 knots. As a result, not expecting any severe weather potential.
Expectations for any thunderstorm activity would be pulse type
activity with at least an entry chance for hail. Heavy rainfall will
also be possible with very little cell movement.
Friday...Large scale pattern will become very conducive for
retrograding upper level high pressure closing off over the western
and central Great Lakes. High confidence exists in dry weather
Friday. Temperatures Friday will again be very warm in the middle to
upper 80s, readings some 15 degrees above averages.
An expansive surface high pressure system sitting over the eastern
third of the U.S. along with an amplified upper-level ridge will
continue to bring hot, dry conditions to Michigan throughout the
weekend and into early next week. Long range models continue to
support 850 mb temperatures that average 17 - 18 degrees Celsius.
Warm air aloft along with southerly flow and generally clear skies
will support daytime highs that peak in the mid to upper-80s. For
reference, record highs range from the upper 80s to low 90s across
Southeast Michigan for this time frame.
The next chance for precipitation and closer to seasonal
temperatures will return on Wednesday, as a cold front acts to
produce the slight chance for rain and thunderstorms. Cooler air
behind the front will act to keep daytime highs capped in the mid to
upper 70s. While too early to say with high certainty, seasonal
temperatures will look to stick around into next weekend.
High pressure will dominate the area through the next several days
with south to southeast winds generally under 15 kts. Lake St Clair
and Lake Erie winds will be more generally out of the southeast and
lighter than the winds in the open waters of Lake Huron. Winds are
expected to remain generally under 15 kts through the weekend as
high pressure drifts in over Lower Michigan.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
841 PM CDT Wed Sep 20 2017
Updated for evening discussion.
Most of the convection has died down now and skies continue to
clear. Those areas that saw rainfall today are already seeing
temperatures in the low 70s. Those other locations are still in
the upper 70s. Overall, temps will fall to the upper 60s and low
70s tonight. Some patchy fog will again be possible tomorrow
morning. Cleared out most of the pops in the forecast with this
Prior discussion below:
Tonight through Thursday...
Latest RAP satellite imagery showed a weak shortwave moving into the
region. This combined with some cooling aloft and low level moisture
had triggered scattered showers and some thunderstorms across the
region. With 6-7c lapse rates we may see a few strong storms with
some gusty winds for the remainder of the afternoon. Expect the weak
shortwave to exit the region by late tonight. For early this evening
the last of the showers will end across the northwest and south. For
later tonight expecting another round of patchy fog prior to dawn
which will lift by 14z. Another weak shortwave from the west will
push through on Thursday. Return flow ahead of this feature will
trigger isolated to scattered showers and thunderstorms mainly
during the afternoon. Once again midlevel lapse rates will be from 6-
7C with weak flow. This could bring a few strong storms with some
gusty winds during the afternoon.
As far as temperatures are concern readings will continue to be
above normal. Lows will be in the upper 60s to lower 70s. Highs will
be in the upper 80s to lower 90s. Heat indices will range from the
middle 90s to around 100./17/
Thursday night through Wednesday...
The period will start out with a highly amplified pattern over the
CONUS as a deep longwave trough digs across the western portion of
the US. This will in turn amplify downstream ridging over the mid-
Mississippi River Valley and Midwest. This ridging will keep the
warmest temperatures in place through the weekend with highs in the
low 90s before an upper low retrogrades beneath the ridge and into
the ArkLaMiss by the start of next work week. These lower heights
will help keep temperatures a few degrees cooler with highs topping
out in the upper 80s through the middle of the week. A cold front is
progged to move through the area next Thur/Fri with a stout
shortwave diving through the Northern Plains helping to reinforce a
more fall like airmass across the area. In terms of precipitation,
isolated to scattered diurnally driven afternoon showers and storms
can be expected through the weekend with the greatest coverage along
and south of I-20. While some isolated activity could linger into
early next week, drier air wedging in from the east will help to cut
back on coverage with any isolated showers and storms confined
mainly to the Delta. /TW/
00Z TAF discussion:
Isold TSRA were noted just north of GTR and between I-20 and HWY
84 at 2330Z. This activity wl dissipate by 21/02Z and VFR conds wl
prevail areawide until 10Z. After 10z MVFR vsbys wl be psbl
areawide until 14Z. After 14Z VFR conds wl prevail until Isold to
Sct TSRAs develop Thu aftn and cont into early evng. /22/
.PRELIMINARY POINT TEMPS/POPS...
Jackson 70 93 71 91 / 9 30 9 27
Meridian 70 93 69 90 / 11 30 16 30
Vicksburg 71 92 71 91 / 8 21 5 18
Hattiesburg 69 91 69 90 / 15 29 17 34
Natchez 70 91 70 90 / 15 25 11 29
Greenville 71 93 70 92 / 8 17 5 17
Greenwood 71 93 71 91 / 8 19 5 17
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
625 PM CDT Wed Sep 20 2017
1246 PM CDT
Through Thursday afternoon...
Concern is on convective development late this afternoon/early
evening and how far east/south it will make it, along with hot
and humid conditions that look to persist for the coming days.
It is indeed hot and humid for mid September, and ORD/MDW are
already almost at 90 degrees today. Warm south winds and little
cloud cover will allow most locations to get close to 90 today.
Convective temperatures on the RAP are in the 90s across IA,
which looks to delay any initial convective development near the
cold front until late this afternoon. There is pretty good
agreement though that thunderstorms will develop between 5 and 6
pm near the Mississippi River. The question will be with the upper
forcing being a bit weaker farther east, and with the convection
arriving around sunset or so, that should limit the eastward
thunder concerns with this initial development. There could be
some sprinkles that get closer to Chicago but the forcing does not
appear to overcome dry mid levels.
While west/northwest IL is favored at this time, the low level
jet will ramp back up in this high PWAT environment, which could
lead to an uptick in showers and storms late this evening/early
overnight hours. PWATs near the front remain elevated and do
increase, so if showers and storms do get a bit closer, some
modest rain rates could occur in the far northwest.
Upper level heights rebuild tomorrow, and continued deep layer
southerly flow will lift the effective frontal boundary back
northward. The lower level airmass will be on par with today`s if
not a bit warmer, and thus many areas will likely tag 90 or even
the lower 90s. These are near record levels for mid to late
September. With continued upper 60s to around 70 dewpoint, this
places heat indices in the middle or even upper 90s.
Thursday night through Wednesday...
155 pm...A warm frontal boundary will lift back north of the area
Thursday night with hot and humid conditions continuing into this
weekend. Bumped up high temps both Friday/Saturday to near
guidance which is generally in the lower 90s Friday and around 90
Saturday. Given high temps today/currently are around 90...these
forecast high temps for Friday and Saturday may end up being a few
degrees too cool. Not expecting much change to dewpoints either...
in the mid/upper 60s thus heat index readings could reach the
mid/upper 90s...at least for a few hours during peak heating in
the early/mid afternoons. Thermally...conditions cool slightly
Sunday/Monday but its possible that with little change to this
pattern the models may trend warmer into early next week. No
change to highs in the 80s Sunday/Monday...but these could also
end up too cool.
Dry conditions expected until a cold front arrives Tuesday night
next week which will bring the next best chance of rain. Much
cooler air will spread into the region behind this frontal
boundary by Wednesday afternoon/evening. There may also be an
isolated shower Sunday/Monday but chances are below mentionable
from this distance. cms
For the 00Z TAFs...
Primary aviation concern this TAF cycle is with SHRA/TSRA
chances. Storms have developed from eastern IA north into WI ahead
of a weak cold front. All indications are that this activity will
dissipate before reaching the immediate Chicago terminals, with
best chance of impacts being at RFD. Have maintained a short tempo
at RFD this evening to cover this threat. Otherwise, where skies
clear overnight, could see some light fog/MVFR vsby, especially in
the more rural areas like GYY/DPA. Otherwise, look for VFR
conditions and light to moderate south winds through the TAF
155 pm...Strong low pressure over western Manitoba will slowly
weaken tonight and Thursday as a weak trailing cold front moves
south across Lake Michigan tonight into Thursday morning. This
front is expected to stall over central portions of the lake then
move back north as a warm front by Thursday night. A large trough
of low pressure will remain nearly stationary across the plains
through early next week which will maintain southerly flow across
the lake. This trough/front will move across the Great Lakes
region Tuesday night next week shifting winds to the northwest
when a period of 15-25kts is expected. cms
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Area Forecast Discussion
National Weather Service Miami FL
809 PM EDT Wed Sep 20 2017
Showers and thunderstorms will continue in the interior through
the evening hours. they are not currently forecast to impact any
of the TAF sites across South Florida. Tomorrow will see another
round of convection. However, there is too much uncertainty as to
the coverage and if they will impact any TAF sites to include in
the forecast attm.
.PREV DISCUSSION... /issued 424 PM EDT Wed Sep 20 2017/
Latest IR satellite imagery shows a band of scattered low level
cumulus stretching east to west across central Florida. In
addition, a line of of building cumulus can also be noted around
10 miles inland from the Atlantic coast, where the sea breeze has
managed to penetrate. Light overall flow will allow for sea
breeze collisions to develop, similar to yesterday. The HRRR is
hinting that the associated slow moving showers and isolated
thunderstorms will continue over the interior through this evening.
Besides a couple showers remaining over Palm Beach county
tonight, where most of enhanced instability and moisture resides,
expecting relatively dry conditions elsewhere. Maximum
temperatures are topping out in the upper 80s along the east coast
and low 90s inland, typical for this time of year.
Thursday through Saturday: Synoptically little changes tomorrow
with both ridging to the north and surface high pressure
dominating. Light easterly winds and a modest amount of moisture
will lead to a chance of showers and isolated afternoon
thunderstorms, mainly over the interior where the sea breeze
collision occurs. From Friday through this weekend, Hurricane
Maria will edge toward the southern Bahamas then northward over
the open mid Atlantic Ocean. There appears to be no direct impact
to South Florida at this time. However, the aforementioned
Hurricane will help to advect deeper tropical moisture into our
region, as well as increase deep northeasterly flow. Thus, expect
better coverage of showers and storms Friday into Sunday,
especially along the eastern portion of the peninsula.
Early next week: As Hurricane Marine continues to barrel northward
over the Atlantic, drier air will be pulled down into our CWA. GFS
PWATs drop to between 1.5" and 2.0". Subsidence aloft should
suppress much of the convection, leading to a drier long term
Long period northeasterly swell from distant Hurricane
Jose will continue to filter into the local Atlantic waters keeping
cautionary conditions in the waters off Palm Beach County into
Thursday. Light and variable winds today will allow both seabreezes
to form this afternoon. Winds will gradually increase out of the
east on Thursday and become turn more northeast or northerly by
Long period northeasterly swell from the distant
Hurricane Jose will continue to filter through the local Atlantic
waters. A high risk of rip currents will continue for all the
Atlantic beaches through this evening, and likely remain moderate to
high into late week.
.PRELIMINARY POINT TEMPS/POPS...
West Palm Beach 76 90 77 90 / 30 30 30 50
Fort Lauderdale 79 91 79 89 / 20 30 30 50
Miami 78 92 78 90 / 20 30 30 50
Naples 76 92 75 91 / 20 30 20 40