Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/25/20
AREA FORECAST DISCUSSION
National Weather Service Albany NY
1044 PM EDT Thu Sep 24 2020
A weak weather disturbance will cross the region tonight with
perhaps a shower to the west and north of Albany under variable
cloudiness. Warmer and slightly more humid conditions arrive
Friday and continue into the weekend. The next chance for some
needed rainfall arrives during the first half of next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 1040 pm, patchy cirrus overhead across the forecast area,
with also some altostratus from about the I-90 corridor back
into the Tug Hill and into southern Ontario advecting into the
region. Expect partly to mostly cloudy skies to continue at
least into the first part of the night. Fog potential will be
tied to whether we see meaningful breaks in these clouds. We
have already seen temperatures falling to near the dewpoint, so
it appears we will see some areas of fog overnight.
As of 330 PM EDT...Our region is within a confluence as two
weather systems were passing by to the north and south of the
cwa. Some surface based instability across western NY and Lake
Ontario along with lake-land convergence is resulting in
isolated to scattered convection this afternoon. SPC mesoscale
window suggest SBCAPES were above 1000 J/Kg with 500 J/Kg just
to west of KUCA as of 19Z. Mesoscale trends suggest these
convective elements upstream should weaken as they track
eastward into eastern NY this evening. So we will continue with
the slight chance PoPs for portions of the Mohawk Valley and
Dacks. Otherwise, main issue will be cloud coverage or
perception thereof as cross sections within BUFKIT and low level
mean RH fields from HRRR point toward a SCT-BKN stratus deck
across a good portion of the region tonight. However, as seen in
the visible imagery, seems we should be able to hold off with a
mostly cloudy forecast so partly cloudy will be placed in the
forecast/grids. Some patchy fog will once again be possible as
winds decouple and dewpoint depressions narrow. Overnight lows
should generally be in the 50s region-wide.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Friday, the weak weather disturbance and rather diffuse frontal
zone across the north tier of NY are expect to be east and
advect north, respectfully. This will leave us within an
increase southerly flow through the day as low level troposphere
continues to moderate a couple more degrees. As forecast mixing
layer heights are expected to be just below H850 where around
+12C resides, we should see valley temperatures climb well into
the 70s to near 80F with mainly 70-75F for higher terrain aob
Friday night, appears to be a tranquil night across most the
region. Exception remains near the I84 corridor toward sunrise.
Upper low along the I70/I64 corridor is forecast to track
eastward and near the mid-Atlantic coastline by sunrise. Low
level trajectory increases slightly from the south to warrant
the continue chance for a shower for the southern zones.
Otherwise, patchy fog once again overnight with lows mainly into
Saturday, the aforementioned upper low tracks just north of east
into the western Atlantic through the day. Low level moisture
transport is weak yet consistent where the previous excellent
forecast suggested 20-30% PoPs for the eastern 2/3rds of the
CWA. We will not deviate too much with this update as clouds
will likely be on the increase for most of the region through
the day. This will cut back on the insolation a bit as daytime
highs, while still mild, might be a degree or two cooler than
those observed on Friday.
Saturday night, further increase of the southerly flow as
subtropical high builds across the southeast Conus and potent
short wave and jet tracks north of the western Great Lakes
region. Low level moisture remains a bit high as we will keep
mostly cloudy skies for areas along and east of the Hudson River
Valley. Due to the cloud coverage and higher lower level
moisture/dewpoints, it will feel rather mild and muggy overnight
with lows ranging from the lower 60s into most valley locations
to mid-upr 50s elsewhere.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Models suggest the upper level flow pattern over the CONUS becomes
more amplified with time during the long term. The period starts out
Sunday with anomalous ridging from eastern New York into New
England, with 500 mb heights possibly near 585 dam. Possibly some
low clouds around in the morning, but assuming they break up, a very
mild day is expected with valley temperatures likely reaching the
80s. Ridging may break down slightly Monday with a shortwave trough
embedded in southwesterly flow, but a mild and moist airmass will
remain in place with PWATs possibly exceeding 1.50 inches (in excess
of +1 standard deviation). Will continue to carry chance PoPs for a
scattered shower-type scenario.
Predictability decreases Tuesday onward. Models generally agree in
anomalous ridging over much of the western US, and a deepening
trough downstream encompassing much of the area from the Great Lakes
into the Deep South. Several pieces of energy will likely be
involved in digging out this trough which can`t be resolved with
much confidence at this time frame, so there is uncertainty with the
eastward progression of the longwave trough. There is disagreement
among the deterministic GFS/ECMWF, not much run-to-run consistency
with the deterministic models, and spread among the GEFS members is
high. Deterministic models have depicted a rather strong cold front
and associated precipitation event in the Tuesday/Wednesday
timeframe, with an attendant drop in temperatures behind the front.
As models often overdo the eastward progression of deep longwave
troughs (particularly the GFS), have avoided any likely PoPs for
Tuesday and increased PoPs into the chance range for Wednesday.
There is potential for needed rainfall of at least moderate
magnitude in this timeframe given potentially strong forcing
interacting with a moist prefrontal airmass.
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Through 00Z/Sat...VFR conditions prevail this evening under high
cirrus. Challenge tonight is determining fog potential.
Dewpoints are relatively elevated in the mid-50s, and winds
should go calm after sunset (except perhaps at KALB which could
see a light southerly wind). The main uncertainty arises from
the extent of midlevel clouds drifting into the area from the
northwest, which satellite imagery suggests are fairly
widespread. Will retain fog mention (IFR at KGFL/KPSF and MVFR
at KALB/KPOU), but confine it to 09-12Z in the event these
clouds dissipate late.
After any morning fog dissipates, VFR conditions will prevail
Friday with just some few-sct midlevel CU/AC/AS.
Winds will be calm to light southerly overnight, becoming south
to southwest at 5 to 10 kt Friday.
Friday Night: No Operational Impact. NO SIG WX.
Saturday: Low Operational Impact. Isolated SHRA.
Saturday Night: No Operational Impact. NO SIG WX.
Sunday: No Operational Impact. NO SIG WX.
Sunday Night: Moderate Operational Impact. Chance of SHRA.
Monday: Moderate Operational Impact. Chance of SHRA.
A weak weather disturbance will cross the region tonight
with perhaps a shower to the west and north of Albany under variable
cloudiness. Warmer and slightly more humid conditions arrive Friday
and continue into the weekend. The next chance for some needed
rainfall arrives during the first half of next week.
RH values will climb to between 90-100 percent overnight with
areas of dew formation and patchy fog. RH should fall to 45-60
percent Friday afternoon.
Light and variable winds tonight, then become south to
southwest by Friday afternoon at 5-10 mph.
Latest drought monitor shows a slight adjustment westward of
intensity (D0-D1), most notability across western New England,
into the I84 corridor and portions of the Taconics. Otherwise,
no hydrologic concerns through this weekend as any shower
activity will be light and have no impacts on water levels. The
next chance for more widespread and needed rainfall arrives
during the first half of 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
Area Forecast Discussion
National Weather Service Boise ID
838 PM MDT Thu Sep 24 2020
Our CWA will stay dry through midday Friday. A storm in the
Pacific near 45/135 is racing eastward under strong zonal flow
and will reach our CWA late Friday and especially Friday night.
This storm promises rain for most areas but especially in the
north where the Buck wildfire is. The fire and the rest of the
west-central Idaho mountains should receive about a half inch
of rain by early Saturday. After this storm exits late Saturday
the upper ridge will rebuild and last through the coming week
with another long period of warm, dry weather. This is all
well-covered by the current forecast. The smoke has cleared but
the HRRR model brings a brief resurgence to southeast Oregon
Friday morning before the Pacific storm comes in. The storm
will then push all the smoke out at least through Sunday.
Mainly VFR. Rain showers spreading into Baker County/Oregon and
the west central Idaho mountains Friday afternoon, then south
across southeast Oregon and the Snake River Valley Friday night.
Surface winds variable 10 kt or less, becoming west 10-20 kt
Friday afternoon and evening, with gusts to around 30 kt. Winds
aloft near 10k feet MSL 20-35 kt.
Weekend Outlook...Mainly VFR. Showers will continue on Saturday,
mainly in Baker County/Oregon and the west central Idaho mountains.
Snow levels 7k-8k feet MSL. Showers will end Saturday evening.
Expect breezy west to northwest winds through the Snake River
Valley Saturday afternoon and evening. Skies will be mostly clear
late Saturday night through Sunday.
SHORT TERM...Tonight through Saturday night...Clouds will remain
across the region tonight into Friday ahead of the next system for
Friday night/early Saturday. Breezy conditions this afternoon will
diminish after sunset. Next system will bring showers to our
northern zones Friday afternoon which will spread southward into
the Western Snake River Plain by early Saturday morning. The West
Central Mountains could see up to a half an inch of rain through
Saturday with the valleys seeing less than a tenth. Cold
northwesterly flow will keep temperatures below normal on
LONG TERM...Sunday through Thursday...Models have trended a
little farther west with the upper level pattern on Sunday, with
a strong upper ridge centered off the northern California coast
and an upper trough diving through the northern Rockies and into
the northern Plains. As a result, temperatures will remain about
5 degrees below normal on Sunday, but dry conditions are expected.
Models continue to show the upper ridge amplifying and shifting
over the West Coast early next week, pushing the jet stream north
into Alaska and northern Canada. Temperatures will climb back to
around 5-10 degrees above normal next week. Our location east of
the ridge axis as well as northwesterly flow aloft will help to
confine even warmer air associated with the ridge to our west.
Mostly clear skies will prevail with no chance of precipitation
through the week.
PREV SHORT TERM...JDS
PREV LONG TERM....ST
Area Forecast Discussion
National Weather Service Charleston SC
1017 PM EDT Thu Sep 24 2020
Rain chances will increase on Friday as remnants from Beta and
an upper-level trough track just north of the region. A cold
front will approach the region early next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 10 PM: KCLX continued to detect a few weak returns across
the forecast area this evening. The latest run of the HRRR
indicated isolated to scattered showers will occur from time to
time tonight. The forecast will be updated to adjust PoP timing
and placement, especially toward latest radar trends. In
addition, hourly temperatures will be updated to align with
As of 725 PM: KCLX detected a few light showers passing over the
inland counties with smaller showers over the nearshore waters.
The showers will likely continue through most of this evening,
then favoring the far inland counties late. The updated forecast
will feature higher PoPs and greater sky cover.
The remnant low of Beta, currently near central MS/AL late this
afternoon, will track northeast into the Tennessee River Valley
tonight while weakening. Moisture will continue to advect into
the local area and PWats are forecast to rise to around 2
inches. As this occurs and isentropic ascent takes place, there
should be an uptick in shower coverage, especially late tonight
towards early Friday morning. Instability remains pretty low so
we kept mention of thunder out of the forecast. Temperatures
will be quite mild by late September standards. Lows are
forecast to range from the upper 60s inland to mid 70s at the
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Friday through Sunday: High pressure builds in the Atlantic, as the
remnants of Beta to our west weakens as it tracks toward the
Northeast. Its associated upper-level trough gradually lifts as it
shifts to the east; staying north of our forecast area. Guidance
shows upper-level forcing concentrated to our north as well;
however, weak DPVA and upper divergence could brush our forecast
area. In addition, the dry air mass that has been in place the past
few days will be disrupted by a line of deep tropical moisture that
trails Beta to the south. Because the bulk of strong forcing for
ascent remains over the Mid-Atlantic states, the greatest chances
for unsettled weather Friday is over the SC/GA inland counties.
Relatively rapid destabilization of the atmosphere will support
scattered showers and thunderstorms. A few thunderstorms could
become organized/severe with with ample shear and moderate
instability (SBCAPE up to 3000 J/kg further SE) with the target area
being southeast GA. An isolated tornado cannot be ruled out;
however, damaging winds are the most likely hazard. In addition, WPC
has placed our forecast area in a marginal risk on Friday for
excessive rainfall considering PWATs increase to 2.25".
This weekend, ridging over the Atlantic erodes and a weak flow
pattern sets up. Centered between anticyclonic flow offshore and
weak cyclonic flow over western GA, low-level convergence will
promote showers and thunderstorms to continue. However, the severe
potential is lower this weekend with less instability and drier air
pushing in as a cold front approaches. Wet ground soil, weak surface
winds, and some slight clearing are all favorable conditions for
radiational fog early Saturday/Sunday morning in the inland GA
counties. The potential for fog depends more so on the likelihood of
cloud coverage; greater clearing would increase fog coverage,
allowing it to creep toward the coast. Temperatures will feel more
summer-like with highs in the mid to upper 80s and lows in the upper
60s/mid 70s through the weekend.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Overall, there is still some model inconsistency on how much deep
moisture will remain situated over the area as a cold front
approaches from the northwest. The first cold front also looks to be
a bit slower approaching the area on Monday then swiftly moving
through by early Tuesday morning. After the front passes through,
the GFS has drier air while the ECMWF now keeps things pretty moist,
with PWATs above 2.0 inches. Therefore, have maintained chance POPs
on Monday. Tuesday looks to be mostly dry before a second cold front
edges closer to the region. Models are still showing a deep trough
forming and trekking across much of the central to eastern US.
Though, less moisture looks to be associated with the cold front as
it moves through the area on Wednesday. Temperatures will continue
to decrease through the week and by Wednesday highs will be in the
upper 70s to low 80s. Lows are expected to dip back into the upper
50s to low 60s.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected through the 0Z TAF period. Light
showers may pass near the terminals late tonight into Friday
morning. Stronger showers are forecast to develop during the
afternoon, with the potential of lower vis during downpours. The
18-22Z timeframe will be highlighted with a TEMPO for MVFR vis
Extended Aviation Outlook: Over the weekend, flight restrictions
are possible in showers/thunderstorms as well as in the late
overnight/early mornings if patchy ground fog develops.
Prevailing VFR conditions should return by early next week.
Tonight: Southeast to south winds will persist tonight. There
will be an uptick in speeds after midnight, but conditions will
remain below Small Craft Advisory criteria. Seas will average
Friday through Sunday: Southeast winds will prevail
through late week as high pressure builds over the Atlantic. Winds
should remain below 15 kts through the weekend with seas 1 to 3 ft
in the nearshore waters and 3 to 4 ft in the outer Georgia waters.
Scattered showers and thunderstorms are possible this weekend caused
by the remnants Beta.
Rip Currents: As the dominant swell period continues to decrease,
the trend for elevated rip currents should continue to decrease as
well. A moderate risk remains in effect for the beaches through
Friday and Saturday`s forecast drops to a low risk.
Area Forecast Discussion
National Weather Service State College PA
1042 PM EDT Thu Sep 24 2020
A large area of high pressure will remain off of the east coast
through the upcoming weekend. Increasing meridional upper level flow
is expected by early next week, as a deepening trough forms
over the plains and an upper ridge builds off the east coast. At
the surface, a slow moving cold front is likely push through
Pennsylvania either Tuesday or early Wednesday.
.NEAR TERM /THROUGH FRIDAY/...
Large surface high centered near Bermuda will ensure fair
weather and light wind across central Pa tonight. Evening
satellite loop and latest RAP suggest cirrus linked to the
remnants of Beta will continue to stream into southeast Pa
overnight. Elsewhere, mainly clear skies and associated radiational
cooling should lead to patchy valley fog late tonight, as the
latest NAMNest and SREF prob charts indicate. Min temps around
sunrise will vary from the upper 40s in the northern mountains,
to the 50s elsewhere.
Latest guidance indicates the high cloud shield from Beta will
continue to affect southern Pa on Friday. Otherwise, expect
mainly sunny skies, filtered through a bit of upper level smoke
from western fires. Last visible satellite images of this
evening show the smoky skies across the Ohio and western Pa.
Max temps are expected to be a couple of degrees higher than
today due to increased sunshine, southerly llvl flow and very
similar, mean 925-850 mb temps with vertical mixing through that
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
Following a good deal of cloud cover early Saturday as the
remnants and precipitation associated with Beta pass southeast
of PA Dutch Country, should see mostly sunny skies return
through the afternoon as temperatures warm into the mid-upper
70s. Backing southwest flow aloft will take shape for the second
half of the upcoming weekend as troughing digs through the Great
Lakes and Ohio Valley and ridging builds over the western
Atlantic, helping promote temperatures climbing well above
normal into the upper 70s to mid 80s in spots Sunday.
.LONG TERM /MONDAY THROUGH THURSDAY/...
All medium range guidance shows increasing meridional flow
early next week, as a deepening upper level trough forms over
the plains and an anomalous upper ridge builds over the western
Atlantic. At the surface, a slow-moving cold front will likely
approach Monday, then cross the state either Tuesday or early
Wednesday. Latest EC/ECENS are slower with the front than the
NAEFS. Have therefore gone with an increasing chance of showers
Monday PM, but the best chance of rain looks to be with the
fropa either Tuesday or Tuesday night. Latest GEFS suggest
rainfall will likely not be heavy enough to put much of a dent
in rainfall deficits across central Pa. However, given the
synoptic pattern of a deep trough and slow moving cold front
tapping Gulf of Mexico moisture, wouldn`t be surprised if some
parts of the region see 1+ inch amounts.
A period of chilly weather with scattered showers over the
northern and western mountains appear likely late next week, as
anomalous upper level trough swings into the northeast CONUS.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
VFR conds, mainly clear skies and light winds expected overnight
into Friday. The one potential issue, though, is patchy low
clouds and fog during the pre-dawn hours (generally 08-12z). It
appears that KBFD and KIPT have the best chance of seeing
Surface winds should average 5 kt or less.
Sun and Mon...Potential brief restrictions in scattered
Tue...Restrictions more likely, with more persistent showers
Area Forecast Discussion...UPDATED
National Weather Service Peachtree City GA
834 PM EDT Thu Sep 24 2020
Only minor tweaks to forecast based on trends and recent guidance.
Will have to watch NW counties for heavy rain threat next few
hours as rain rates creeping up and favorable moisture advection
pattern expected. Treat for any severe storms diminishing a bit
over SE AL and WC GA this evening. Line of convection in eastern
AL somewhat shallow in spite of good low level moisture
advection and marginal to adequate vertical wind shear and
.PREV DISCUSSION... /Issued 314 PM EDT Thu Sep 24 2020/
SHORT TERM /Tonight through Friday Night/...
Remnants of Beta definitely making the entry into the region
today. As discussed on yesterday`s AFD, the Hi-res WRF was picking
up on the wedge being reinforced as the low approaches and east
winds increase. The result is a baroclinic zone setting up along
the I-20 corridor by which the remnant low from Beta travels
resulting in slightly more rainfall totals across N GA because of
a further south deformation zone. A second low forms over Northern
AL which is separated from the moisture axis and is the
reflection of the upper level trof trailing Beta...and will be the
reason we don`t clear out quickly behind Beta. Several other hi-
res models also picking up on this including the HRRR and NAM 3KM.
Overall...it won`t change our thinking but rainfall amounts have
ticked back up across the northern part of the state with the HRRR
suggesting some spots over 3" are possible across NW GA. Once the
low passes, will have plenty of low level moisture in place
setting us up for 2 nights of patchy dense fog including overnight
tonight. Opted to not issue dense fog advisory for tonight but
can`t rule out areas of fog. Looks as though Friday night has a
better chance for widespread fog given the near 100 pct RH
LONG TERM /Saturday through Thursday/...
As the shortwave trough and remnants of Beta continue moving east of
the Appalachians, an upper level ridge will develop over much of the
southeastern CONUS on Saturday. This ridge, and associated high
pressure at the surface, will inhibit rain chances throughout the
day on Saturday, with the exception of some slight chance PoPs
lingering across eastern Georgia during the morning hours. Lesser
cloud cover underneath this ridge will allow high temperatures to
climb back into the low to mid 80s across the forecast area on
Saturday afternoon, which will be slightly above the climatological
Another transition in the pattern is anticipated on Sunday as the
upper ridge moves eastward towards the Atlantic coast and a
shortwave trough enters the Mississippi Valley. As this trough nears
Georgia, the upper level flow will become southwesterly, which will
lead to moisture return over the forecast area. Isolated to
scattered showers and thunderstorms will return on Sunday afternoon
and through the day Monday. A deepening longwave trough will swing
southeastward from the Great Plains towards the Mississippi Valley
region during the day Monday. A surface low associated with this
trough will extend a cold front into Georgia.
Model discrepancies remain with respect to the timing and
development of this system. The latest GFS solution brings the front
into northwest Georgia on late Monday and moves it quickly through
the forecast area. In contrast, the latest ECMWF indicates the
trough developing into a deep cutoff low over the southeastern CONUS
and bringing the front into the forecast area more slowly, later
Tuesday into the overnight hours. The ECMWF furthermore indicates
considerably more precipitation ahead of the cold frontal boundary.
As such, have maintained chance PoPs in northern Georgia and slight
chance PoPs elsewhere in the forecast area on Tuesday to account for
the ECWMF solution. Due to this lingering uncertainty, this system
will require continued monitoring.
A cooling and drying trend will be underway during the middle of
next week behind the front. High temperatures will be in the 70s
across most of north and central Georgia Wednesday afternoon and
range from the mid 60s to mid 70s next Thursday -- about 6 to 10
degrees below climatological normals. Dewpoints will similarly drop
into the upper 40s and low 50s areawide by Wednesday afternoon. With
these cool and dry conditions and minimal PoPs, a couple of pleasant
autumn days could be in store next Wednesday and Thursday.
IFR cigs and vsbys expected to go down to LIFR this evening at ATL
metro airports and later at other forecast points. Sfc winds will
continue E 8-12kts before becoming SW after 14Z or so at ATL metro
locations and later at KCSG/KAHN/KMCN. Sct -SHRA will persist
with DZ in between. Improvement in cigs/vsbys expected after wind
shift with decrease in coverage of precip.
//ATL Confidence...00Z Update...
Medium on cig, vsby and precip timing
High confidence on all other elements
.PRELIMINARY POINT TEMPS/POPS...
Athens 64 78 65 81 / 90 60 30 10
Atlanta 66 78 65 82 / 90 40 20 10
Blairsville 59 72 60 77 / 90 60 40 10
Cartersville 65 78 64 83 / 90 50 10 10
Columbus 70 82 66 85 / 80 30 10 10
Gainesville 62 75 64 80 / 90 60 30 10
Macon 69 83 67 85 / 60 50 20 10
Rome 65 76 64 83 / 90 50 10 10
Peachtree City 68 79 64 82 / 90 40 10 5
Vidalia 71 86 70 88 / 30 60 40 10
Area Forecast Discussion
National Weather Service Grand Forks ND
940 PM CDT Thu Sep 24 2020
Issued at 940 PM CDT Thu Sep 24 2020
A few of the cells associated with the system moving to the east
across north-central ND and southwest MB have been producing
lightning this evening. According to the RAP analysis, MUCAPE is
around 500 J/kg in this area of stronger cells. The HRRR brings an
axis of 500 J/kg MUCAPE through the area...so introduced a slight
chance of thunderstorms along with the showers tonight and
tomorrow as the activity pushes east through northern MN. The
threat associated with these weak thunderstorms will be any
lightning that might be produced.
UPDATE Issued at 658 PM CDT Thu Sep 24 2020
Showers will move into the region late tonight associated with an
upper level wave moving east across MB and ND. Mid level frontogenesis
looks strong with this wave as well...leading to the strongest
shower activity between 6 AM and noon across far NW MN including
the Lake of the Woods area. There is a low chance of fog in the
Bemidji to Wadena area tonight, but confidence remains low right
now. Believe there will be an area of low clouds continuing in
this area tonight...and perhaps some light fog/mist at times. For
the most part, no weather-related impacts are expected tonight or
.SHORT TERM...(This evening through Friday night)
Issued at 225 PM CDT Thu Sep 24 2020
No big impacts to worry about in the short term. The stratus deck
lifting this afternoon has been the biggest challenge, left over
from the fog this morning. Grand Forks took forever to finally
scatter out, and satellite imagery still shows fairly thick
stratus around Detroit Lakes, Park Rapids, and Bemidji. This
Minnesota lakes area stratus may linger for a few more hours yet,
until winds pick up a little more. Otherwise, still expect some
shower development overnight into Friday morning. There is still a
potential for some areas across northwest Minnesota to pick up
around a quarter of an inch of precipitation. This activity should
shift to the east of the FA by Friday afternoon, leaving Friday
night pretty quiet again.
.LONG TERM...(Saturday through Thursday)
Issued at 225 PM CDT Thu Sep 24 2020
Opportunities for impactful weather will be scarce during this
period, with showery chances at times during the weekend. maybe a
freeze as the forecast period ends ?
Doesn`t seem to be anything overly impressive regarding weekend
activity. A couple of shortwaves will traverse mainly zonal flow
offering scattered shower chances from time to time. Some cooler air
will filter in behind developing northwest flow Sat night limiting
Sun max temps to the 60s.
Later Sun into Mon there will be a pronounced mid-CONUS trough
diving down through the mid and lower Mississippi Valley, certainly
bringing much cooler air to the Northern Plains as the new week
dawns. We will be talking about highs in the 50s for much, if not
all, of the new week. And north to northwest flow will keep chances
alive for periodic bouts of RW.
By the end of the period, ensemble 850 mb temps drop to near or
below zero C. introducing freeze chances for at least the northern
half of the forecast area Thu morning.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 658 PM CDT Thu Sep 24 2020
A large area of low MVFR ceilings exists over north-central MN
this evening. This area was originally expected to dissipate
in the BJI area this afternoon...but latest trends indicate that
it won`t...but rather may expand a bit northwestward. Have opted
to keep cigs low for tonight at BJI...eventually going IFR. An
area of showers will move in from the northwest and expand in area
overnight tonight. Expect showers across northwest MN by morning
...and then exiting the BDE to BJI to ADC area by early afternoon.
Some LLWS will exist overnight as well...mainly in the northern
TAF sites of DVL/GFK/TVF.
Area Forecast Discussion
National Weather Service Marquette MI
829 PM EDT Thu Sep 24 2020
.SHORT TERM...(This evening through Friday)
Issued at 437 PM EDT THU SEP 24 2020
Water vapor imagery and RAP analysis show broad troffing from the ne
Pacific into the Pacific NW, ridging from southern CA to Manitoba
and troffing over eastern N America. Shortwave tracking se thru the
Upper Mississippi Valley was responsible for the shra/tsra that
occurred mainly over far western into s central Upper MI last night
and the lingering shra in that area this morning. With that wave
weakening as heights begin to rise in response to a shortwave
progressing downstream into MT/Saskatchewan, pcpn has diminished
today. However, with the shortwave over WI and clouds breaking a
little to allow for some heating, shra are redeveloping immediately
downstream in WI with some -shra also developing into western Upper
MI. Temps across the fcst area are currently in the upper 50s to
lwr 60s for the most part.
Tonight, heights will be rising across Upper MI as aformentioned
ridging shifts to the Upper Great Lakes in advance of shortwave
moving across the Dakotas/s central Canada. Meanwhile, the Upper
Mississippi Valley shortwave will dive sse. At least into the
evening hrs, will likely continue to see isold to perhaps sct -shra,
mainly from the w into the s central. Then overnight, with low-level
winds veering to the se to s and plenty of lingering low-level
moisture, low stratus and some fog will develop in the areas that
see upsloping. Expect min temps mostly in the 50s.
Fog/low clouds will clear out during the morning, then attention
turns to the shortwave shifting to the Upper Mississippi Valley and
northern Ontario. Ahead of the approaching cold front, southerly
winds will pick up. Fcst soundings suggest wind gusts to 20-30mph in
the aftn. These increasing winds on Lake MI will build waves,
leading a mdt swim risk for the beaches of Schoolcraft County in the
aftn. 850mb thermal ridge with temps of 12-14C ahead of the front
will shift over the area during the day. Although there won`t be
full sun, temps should still top out in the 70s, except 60s close to
Lake MI. Late in the day, cold front will approach Upper MI. Fcst
soundings suggest a capped environment, so shra/tsra should be
confined to close proximity of the front. Have thus held off on pcpn
mention until after 21z over the far w. If sfc based convection does
develop, potential of MLCAPE up to 1000j/kg and deep layer shear in
excess of 50kt will support organized storms and a svr risk.
.LONG TERM...(Friday night through Thursday)
Issued at 347 PM EDT THU SEP 24 2020
Several quick moving weather systems will provide opportunities for
rain Friday night through the weekend with a turn to much cooler
fall-like weather by next week. A weak front will push across the
Upper Lakes Friday night. Any instability will be on the wane Friday
evening but shear profiles are pretty impressive. As shortwave moves
eastward along the Canadian border and the Arrowhead of MN, there
may be enough forcing to overcome the capping in place. Thus, there
is a conditional threat for a few stronger storms over the western
U.P. Friday evening. Any shras/tsras will weaken as they move
eastward through the overnight. Brief shortwave ridging will build in
to the area for late Friday night into Saturday morning before the
next storm system moves into the area later Saturday into Saturday
night. While lots of sunshine is doubtful, a break or two can`t be
ruled out. Regardless, it will be a fairly mild day with highs in
the lower 70s...perhaps the last one for awhile.
As shortwave and surface low/front move across the Upper Lakes
Saturday night into Sunday expect another round of shras and
isolated tsras to affect the area. Post frontal day on Sunday will
be breezy with seasonable temperatures.
Models have continue to trend away from a wrapped up fall storm for
early next week. Trends do continue to favor a cooling trend with
upper troughing increasing across the lakes. The coolest of the area
will arrive mid to late in the week. 85H temps may fall into the -6
to -8C range. Early week 85H temps will be on the 0 to -2C range
which may be enough to generate some lake effect shras from time to
time. For the highlands inland from the lake...the first snowflakes
or at least graupel showers look possible for later in the week
especially Thursday and probably Friday morning with the thermal
troughing at its maximum. All in all...anticipate a very fall-like
week next week.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 827 PM EDT THU SEP 24 2020
Lingering low-level moisture combined with developing light upslope
southerly wind tonight at KSAW will likely lead to LIFR conditions
developing. Although there will be a downslope wind component at
KIWD/KCMX enough moisture remains so that lower end MVFR or IFR cigs
should prevail tonight. KIWD/KCMX will improve to prevailing VFR Fri
morning while KSAW improves to MVFR and finally to VFR during the
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 437 PM EDT THU SEP 24 2020
Winds will diminish across Lake Superior tonight as pres gradient
weakens. However, early this evening, winds may still gust 20-25kt
over western Lake Superior. Southerly winds will increase on Fri
ahead of an approaching cold front. As is usually the case for
southerly winds, the stronger winds will be over the e half of the
lake where gusts to 20-30kt are expected by late aftn and on into
the evening, particularly at high obs platforms and probably toward
and into the nearshore waters e of Marquette. With the passing front
weakening, post frontal winds will fall off to under 20kt Fri night
and to under 15kt across the lake for Sat. A fast moving
developing/strengthening low pres will lift ne across western Lake
Superior Sat night. Winds will ramp up with gusts probably to 25-
30kt. Depending on how quickly the low deepens, a brief period of
gales is certainly not of the question. The potential for a strong
fall storm to affect Lake Superior early next week is diminishing.
However, with colder air flowing into the area, winds will likely be
into the 15-25kt range at times.
Beach Hazards Statement until 10 PM EDT this evening for MIZ005.