Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/24/20
AREA FORECAST DISCUSSION
National Weather Service Albany NY
954 PM EST Mon Nov 23 2020
.SYNOPSIS...
Lake effect snow showers and flurries will continue to
the west and southwest of the Capital District tonight before
diminishing towards daybreak. High pressure will move across the
area on Tuesday with sunny but cold conditions. Another storm system
is forecast to impact the region heading into the Thanksgiving Day
holiday with rain and snow showers.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
As of 952 PM EST...A short-wave is moving across the region in
the cyclonic flow and a secondary cold front will move through
tonight. The low-level flow continues to shift to the northwest
and some lake effect snow showers and flurries have grazed
portions of the western Mohawk Vally, and currently are moving
into the northern and eastern Catskills, and the Schoharie
Valley. The low-level flow trajectory and conditional stability
class favor some multibands. The inversion heights are low
around 5 kft AGL based on the BUFKIT profiles upstream and the
latest 00Z KALY sounding. The latest 3-km HRRR continues to show
the inversion heights lowering and the flow veering to the
northwest, so the activity should continue to diminish 07-10Z.
Some light snow accums of a dusting to a half inch are possible
in a few locations, and perhaps up to an isolated inch over the
higher terrain in a narrow band.
A narrow slot of clearer skies has set up along and north of the
Mohawk Valley into portions of the Capital Region and southeast
into portions of the Hudson Valley, southern Berkshires and NW
CT. Some clouds may fill back later. Sky grids were retooled.
Also some moisture may remain trapped under an inversion north
and west of the Capital District. The winds continue to diminish
with the weakening sfc pressure gradient and the stabilizing
boundary layer. The clear/partly clouds skies have allow temps
to cool off a little quicker in a few spots, so we lowered
temps a few degrees with lows still in the upper 20s to around
30F in the valleys, and upper teens to mid 20s over the higher
terrain.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Big Bubble no trouble through Tuesday as 1030+mb surface high
slides across the region. Should provide ample sunshine between
some stratocu as forecast highs between 40-45F from the Capital
Region and points southward with mainly 30s elsewhere (upper 20s
for portions of the Dacks). As this high slides off the New
England coastline, upstream storm system begins to take shape.
This storm, more or less a potent cut off low developing across
the four-corners region, will send downstream warm advection
regime to unfold. For our region, clouds will be on the increase
Tuesday night as broad isentropic lift is expected to take place
overnight. Difference this model run and HREF is a more broad
potential with overrunning precipitation to evolve toward and
after 06Z/Wed. Cross sections from various NCEP Model Suite
differ with respect to how much low level dry air will remain in
place. Per HREF guidance, we will increase PoPs along and north
of I90 with a period of light snow developing. QPF appears to be
one tenth of an inch or less. Overnight lows mainly into the
20s.
Wednesday, the NAM is the only operational model with surging
the warm advection and drier air into the region. Global models
suggest the warm front may slow or retreat a bit during the day.
The impacts for the region will be either some light
precipitation or keeping conditions dry. We will cut the
difference and keep the front within the CWA and the low chance
for a wintry mix of rain/snow which will be dependent on
boundary layer temperatures. Regardless, not expecting too much
with QPF consensus generally less than one tenth of an inch.
Wednesday night, the aforementioned upper low is forecast to
track into the southern Great Lakes region overnight. Low level
warm advection and isentropic lift will be across the entire
region. Clouds and the threat for additional rain and snow
showers, with the better mixture across the higher terrain.
Here, the QPF does increase a bit more with the best theta-e
advection just to the southeast of Albany. This is where the
higher amounts are in the forecast with at or above one quarter
of inch with lesser values elsewhere. Overnight lows mainly
into the 30s to near 40F closer to the I84 corridor.
Thursday (Thanksgiving Day), this upper low is forecast to
track across the CWA. This will keep the weather unsettled with
additional showers with the best theta-e ribbon to the east of
the CWA. At this time, thunder potential looks low as Showalter
values do drop but remain around 2C within the global models,
near 0C in the NAM south of Albany and mid level lapse rates
are moist adiabatic (slightly higher in the NAM). Highs into the
40s with lower half of the 50s from Albany and points south and
southeast.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A fairly benign pattern is expected for the long period after a
southern stream cut-off low exits our region Thursday night.
Temperatures look to run near to even slightly above normal through
the period as well. Outside of some possible lake effect snow
showers Saturday/Saturday night, the pattern will also generally run
dry before attention turns to a potential system early next week
that may develop in response to southern stream energy and moisture.
Read on for details.
Our cut-off low from Thanksgiving exits into New England Thursday
night. We continue to show slight chance and low end chance POPS for
the Berkshires and Litchfield County before trending dry overnight.
Despite the system exiting, west-southwest flow and continued cloud
coverage retains the mild air mass overhead which is why we expect
overnight lows to only drop into the upper 300s to low 40s. Normal
overnight lows for late November are in the mid 20s.
By Friday, our 850hPa cold front slowly approaches the region but
guidance continues to suggest that weak ridging building in place
will maintain zonal/westerly flow resulting in mild temperatures
once again. Therefore, expecting highs to reach into well into the
50s with only mid to upper 40s in the higher terrain areas.
Guidance is in decent agreement that our mid-level cold front
finally pushes through the area on Saturday. While a few upper level
shortwaves will act as the needed "kicker" to push the front through
the area, the overall upper level forcing remains weak and guidance
suggests the front may not move entirely through the area until late
in the day. Therefore, temperatures Saturday once again may run a
few degrees above normal with highs still in the mid to upper 40s.
Normal highs for late November are only around 40. We kept a dry
forecast for Friday as well due to lackluster mid-level moisture and
weak forcing.
Northwest flow in the wake of the boundary finally ushers in a brief
period of chillier Canadian air Saturday night. With Lake Ontario
still near 10C and 850mb isotherms ranging -3C to -5C, the required
13C temperature difference may barely be met to result in some lake
effect snow showers overnight. Given that the chilly air mass will
only be overhead for a brief period, we maintained a dry forecast
but we will continue to monitor deterministic model trends.
Overnight lows finally cool to more seasonably levels ranging from
the mid 20s to low 30s.
Upper level and surface ridging return for Sunday resulting in
another dry forecast. Northwest flow shifts to the southwest which
allow temperatures to stay near to slightly above normal in the 40s.
Warm air advection increases through the day and into Monday as
surface high pressure moves offshore. Forecast confidence decreases
heading into early next week as there are notable discrepancies
between the deterministic guidance. The GFS and CMC show the
potential for northern and southern stream energy to interact which
may result in secondary cyclogensis occurring off the eastern
seaboard. However the ECWMF show a more suppresses solution which
would keep any coastal development well to our south/east. For now,
we maintained chance POPs over the region for Monday but it`s worth
mentioning that with such a progressive pattern in place, cold air
does not look to be readily available. We will continue to monitor
trends in the coming days and adjust the forecast as needed.
&&
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
An upper level disturbance and a secondary cold front will move
across the region tonight. High pressure will build in for
tomorrow.
VFR conditions are expected the next 24 hours for
KGFL/KALB/KPOU/KPSF ending 00Z/WED. Stratocumulus continue at
some of the terminal sites with the cyclonic flow and lake
moisture being tapped. Cigs are generally in the 3.5-4.5 KFT
AGL. Some moisture may remain trapped under an inversion keeping
the clouds more persistent at KGFL/KPSF/KALB tonight. Some
clearing is likely between 09Z-13Z. KPOU has clouds currently,
but these should erode prior to midnight. The subsidence from
the strong sfc high will yield clear skies in the late morning
through the afternoon.
The winds will gradually subside tonight but will still be west
to northwest at 5-12 kts, except at KPSF where the winds will be
in the 12-18 kt range with some gusts 25-30 kts early tonight
before gradually subsiding to around 10 kts with some gusts
around 20 kts. N/NW winds will be in the 8-13 kt range during
the late morning into the afternoon with some gusts around 20
kts at KPSF/KALB.
Outlook...
Tuesday Night: No Operational Impact. NO SIG WX.
Wednesday: Moderate Operational Impact. Chance of SHRA...RA...SN.
Wednesday Night: High Operational Impact. Likely SHRA.
Thanksgiving Day: Moderate Operational Impact. Chance of SHRA.
Thursday Night: Low Operational Impact. NO SIG WX.
Friday: No Operational Impact. NO SIG WX.
Friday Night: Low Operational Impact. NO SIG WX.
Saturday: Low Operational Impact. Slight Chance of SHRA.
&&
.FIRE WEATHER...
Colder air moving across the warm open waters of Lake Ontario
will bring occasional clouds and some lake effect snow showers
to the west and southwest of Albany. Then, high pressure will
move across the area on Tuesday. Another storm system is
forecast to impact the region heading into the Thanksgiving Day
holiday with rain and snow showers.
The fire weather season ends today. The issuance of this product
will resume in Spring 2021.
&&
.HYDROLOGY...
Outside of some light lake effect activity for portions southern
Herkimer, Schoharie, Ulster and perhaps into Greene...mainly dry
weather overnight into Tuesday evening.
Additional wet weather is expected overnight Tuesday into
Thanksgiving Day. Amounts won`t be heavy, generally under a
half inch, so little hydrologic impact is anticipated at this
time.
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...BGM/Wasula
NEAR TERM...BGM/Wasula
SHORT TERM...BGM
LONG TERM...Speciale
AVIATION...Wasula
FIRE WEATHER...BGM
HYDROLOGY...BGM
Area Forecast Discussion
National Weather Service Denver/Boulder CO
819 PM MST Mon Nov 23 2020
.UPDATE...
Issued at 819 PM MST Mon Nov 23 2020
Still a very challenging forecast for late tonight and Tuesday
morning. The storm total QPF for the 00Z NAM is around 0.87" for
KDEN, while the 00Z run of the HRRR is 0.03". A band of heavy snow
is expected form due to frontogenesis. Snowfall rates of around 2
inches per hour will be possible under this snow band. Seems the
western extent of the models have it over the Denver area. Just
eyeballing the models, the average is over the Palmer Divide to
northern Washington county. Wouldn`t be surprised to see a small
swatch of 5-8 inches if this bands stalls for a few hours. If not,
totals should be closer to 2-5 inches.
Main message is it will be a snowy slick commute for the Denver
area, especially over the western and southern parts. Still
haven`t ruled out adding an advisory to areas east of the current
one, including Denver. Will wait until the 00Z GFS arrives before
making a final decision.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 245 PM MST Mon Nov 23 2020
Satellite imagery shows the increasing southwesterly flow across
the state ahead of the approaching trough digging all the way down
to southern California. Cumulus clouds moving into the mountains are
showing the convective nature ahead of this system, which isolated
to scattered showers are expected to continue over the mountains
this afternoon and evening, increasing in coverage and intensity
toward midnight. Across the plains, the rest of this afternoon and
early evening will have high clouds increasing. A surface low will
begin dropping south allowing for northerly winds to start
spreading across the area with cooler air filtering down.
700-500mb frontogenesis starts showing up well early this evening
up across the northern mountains into Wyoming while QG upward
vertical motion increases. Showers will be spreading across the
plains, but all precipitation should remain rain as the
southwesterly flow aloft keeps temperatures warm enough.
Not until after midnight, does the actual cold front start
plowing down over the area, and the frontogenesis starts moving
south as well, with southwesterly flow aloft remaining. Therefore,
banding is expected to form across the area, most likely near the
I-70 corridor over the mountains northeast out over the plains.
Convection is still possible ahead of the front and band, and
can`t completely rule out a stronger cell with possible thunder.
Forecast soundings show the rain changing over to snow just before
sunrise over the metro areas, somewhere between the 3am-5am time
frame. The aforementioned convective potential may end up stealing
some of the available moisture which may trend down expected
snowfall, however, it could also switch the rain over the snow
earlier, thereby increasing snow amounts. Needless to say,
especially in a banded snow set up, confidence in snow amounts is
low to medium. However, still very much agree with the Advisories
issued due to upslope flow helping the western and southern
suburbs including the Palmer Divide, and the low snowfall amounts
will likely fall in a very short time span - being over the
morning commute. The band will be able to produce snowfall rates
of 1"/hour or more. Initially the snow will likely melt on the
relatively warm pavement temperatures, but then create sloppy
slush with some areas seeing accumulating snow.
The band looks to really have an effect along or south of I-76
corridor and across RMNP and towards Kremmling. North of this,
lower snowfall amounts are expected, especially over Larimer and
Weld counties due to downsloping off the Cheyenne Ridge. Mountains
to the south of the aforementioned area will see the highest
amounts, generally 6 to 12", foothills 3 to 7", plains 1 to 3 ",
except the western suburbs and southern suburbs down onto the
Palmer Divide where 3 to 6 " are expected.
The upper trough will be over the area Tuesday morning and move
east through the afternoon, bringing subsidence and with drier
air moving in from the north. Snow will likely be done and out of
the metro areas by noon, with the eastern plains likely seeing it
for another couple hours. Some remaining moisture in the
northwesterly flow behind the trough will keep light orographic
snow across the mountains.
.LONG TERM...(Tuesday night through Monday)
Issued at 139 PM MST Mon Nov 23 2020
Tuesday night, expect weak subsidence and northwest flow aloft
behind the exiting trough, with increasing winds in the mountains
and foothills. A strong stable layer will develop over the
mountains overnight, with widespread lapse rates around 4 C/km in
the 600-500 mb layer. The wind direction is northwest during the
strongest flow, so we don`t expect a mountain wave to develop, but
are keeping gusts to 40 mph across the highest elevations of the
Front Range mountains into midday Wednesday.
Forecast soundings are starting to show a few hours of fog around
Kremmling in the early morning Wednesday. This has been a common
occurrence after snowfall this season so it merits mention and a
follow up in a closer forecast period.
The ridgetop stable layer and increasing westerly winds aloft
will support the development of a mountain wave early Wednesday
afternoon, which will amplify through the evening as flow aloft
turns more westerly and further strengthens. Strong and gusty
winds exceeding 50 mph are probable in the Front Range mountains
and foothills but a high wind event is not currently expected. Lee
troughing may increase the pressure gradient and cause some of
these gusty winds to spread to the adjacent plains in the evening.
Subsidence is minimal so the winds will likely remain in and very
close to the Front Range foothills. The strong winds should occur
late Wednesday into Thursday morning until winds aloft turn
southwesterly and decrease in strength.
Another trough will come onshore in the Pacific Northwest
Wednesday and advance inland through the day. Flow aloft over
northeast Colorado will turn southwesterly by Thursday morning as
the trough approaches. There will be a slight chance of some light
precipitation in the mountains as the trough moves over the
Rockies Thursday evening and night. Snow accumulation should be
quite limited by a general lack of moisture and modest dynamics.
ECMWF and GFS ensembles have only between 0.1 and 0.2 inches of
precipitable water in the mountains and a QG analysis of
deterministic models showed less than 10 mb/hr of ascent. Lapse
rates are favorable for snowfall for only a short time Thursday
afternoon, thus only a light snowfall in the mountains Thursday
afternoon through Friday morning is expected, with only a few
inches accumulating on even the higher ridges.
The ECMWF predicts the trough will leave a cutoff low over the
four-corners region of the Southwest on Friday as it moves over
the Rockies and out to the Plains. Previous GFS runs agreed with
this solution, but the latest run is waiting until Saturday
morning to drop the cutoff low over Texas and Oklahoma. Thus,
there is higher than normal uncertainty in the forecast for this
weekend.
&&
.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 819 PM MST Mon Nov 23 2020
Northerly winds are expected to continue through the night and
then increase behind a cold front. A few rain showers will develop
later this evening, becoming more widespread after midnight. A
change over to snow is expected in the 2 am to 4 am time frame.
Snow will continue Tuesday morning but should end before noon. At
this time, it appears 2-3 inches of snow will possible at KDEN,
with 3 to 5 inches at KBJC and KAPA. However, snow banding is
expected, so an additional 2 inches will be possible if this band
sets up longer than expected. The threat for snow ends around 18Z.
By 00Z Wednesday, mostly clear skies are expected to prevail.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 AM to noon MST Tuesday for COZ039-
041.
Winter Weather Advisory from midnight tonight to noon MST
Tuesday for COZ034-036.
&&
$$
UPDATE...Meier
SHORT TERM...Kriederman
LONG TERM...Direnzo
AVIATION...Meier
Area Forecast Discussion
National Weather Service Des Moines IA
615 PM CST Mon Nov 23 2020
.DISCUSSION.../Tonight through Monday/
Issued at 253 PM CST Mon Nov 23 2020
Forecast Highlights:
- Wet and wintry period through the first part of Wednesday
- Seasonable and dry Thanksgiving Day
- High degree of uncertainty in forecast late next weekend
Details:
GOES-East upper level water vapor imagery shows a deepening trough
over the Intermountain West early this afternoon with our area under
the influence of a 250mb, ~100 knot, favored for ascent left exit
region. As this trough and a developing area of surface low pressure
over eastern Colorado moves eastward today, will see precipitation
trying to lift into our area. However, this will first have to
overcome a good deal of dry air in the atmosphere, which has
occurred with strong lift over southern Iowa late this morning and
early this afternoon. The 12z OAX RAOB showed this dry air below
450mb, but some saturation was beginning to occur in a shallow layer
around 700mb. Subjectively, the HRRR and RAP soundings seemed to
verify best with the observed sounding with the NAM and GFS to a
slightly lesser degree. The key will be how quickly saturation is
achieved, especially with temperatures rising to above freezing.
Early morning runs from the HRRR and RAP point to early this
afternoon for top down saturation to occur versus late
afternoon/early evening from the NAM and GFS. With snow just
beginning at our office just before 2pm, the winners are the HRRR
and RAP. With the dry air, wet bulbing has been occurring, which has
resulted in a half inch to inch accumulations in our southwest
forecast area so far. Most of this snowfall will accumulate on
grassy areas with some accumulation on roadways if rates can last
long enough to overcome above freezing road surfaces. This wave of
isentropic lift on the 290-295K layer will eventually lift eastward
through this afternoon with primarily snow continuing. Some light
rain is possible, but given we are on the downward slide of peak
heating and dewpoints are hanging in the upper 20s to 30s at this
hour, that will not be common.
Another wave of isentropic lift, which looks even stronger and is
coincident with strong QG convergence, will move over Iowa tonight.
There will be strong moisture transport into the state for late
November with precipitable water values ranging from 0.75" over
northern Iowa to around 1" over central/southern Iowa. While
southern Iowa will predominately see rain as this low level thermal
lift prevails, for northern areas a transition to snow is likely.
Forecast soundings over northern Iowa (e.g. MCW, ALO) reveal that
while surface temperatures may be at or just above freezing, there
is a deep layer in which the temperature profile is in the favored
dendritic growth zone just below freezing with lift maximized toward
the middle to top of this layer. This transition to snow will occur
this evening through the hours around sunrise before transitioning
back to rain. The snow may come down heavily for a time, with the
3z/9z SREF having a small area topping out with probabilities of 40-
50% of 1"/hr rates that develop over our far northeast CWA and more
so points north and east as it departs our area tonight 6-12z
tonight. The 12z HREF has very low, splotchy 1"/hr probabilities as
well, but most of that is over northeast Iowa as well. While ground
temperatures and perhaps even the surface temperature may be 33/32,
the expected precipitation rate at night will overcome this and
cause accumulation. This snowfall will have low snow to liquid ratio
and be wet and sticky given the thermal profile near 0C. There is
potential that if profiles cool quicker this evening and last long
with modest to high rates that accumulations would be higher. While
the timing lowers the impact with the exception of the morning rush
hour, the uncertain in borderline temperature profile leads us to,
in collaboration with WFOs La Crosse and Quad Cities, to issue a
winter weather advisory later this evening through the morning rush
hour over our northeastern areas.
Accumulating snowfall will switch to rain through the morning hours
with any impacts from the snow lessening with time as temperatures
rise above freezing. The rain will generally be on the lighter side
and may at times turn to more of a drizzle, especially over northern
Iowa. As another area of strong QG convergence moves through
northern Missouri and southern Iowa later Tuesday into Tuesday night
ahead of the trough and surface low, will see return to more
persistent rain. The deformation zone on the back side of the low
will have precipitation and soundings still largely support in the
form of rain with GFS showing the most low level warm air as far as
depth and magnitude compared to NAM.
As this surface low moves from Missouri into the western Great Lakes
Wednesday, this will bring an end to the precipitation. Thanksgiving
Day will be dry as a moisture starved front passes with lower
thicknesses following behind and a cooler day on Friday with highs
about 5 degrees lower. Highs will be slightly higher on Saturday
ahead of the next weather system, which deterministic and ensemble
members disagree on the handling of. The 00z ECMWF and the 12z CMC
phases the north and a southern stream wave and generates wintry
precipitation over at least part of the state on Sunday. The 06z/12z
GFS and 12z ECMWF has the northern and southern stream farther apart
and phasing never occurs yielding a dry forecast. 00z ensemble
members are split as well so going forecast will not deviate from
initial guidance. Until the resolution of these differences, there
is a high degree of uncertainty in the temperature forecast ranging
from the upper end in the 40s to the low end in the upper teens or
20s.
&&
.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 607 PM CST Mon Nov 23 2020
Poor aviation conditions abound at area termianls over the next
24 hours as an area of low pressure takes aim on the state.
The period begins, with ongoing area of -SN mainly east of I-35
and south of I-80, primarily impacting KDSM and KOTM with
generally 1-5SM VSBYS. Northern IA terminals will see
deteriorating conditions through 06z as CIGS lower and
precipitation expands across the area. KALO will see the most snow
accumualtions 04-12z, with generally 2-3" expected there.
Elsewhere snow will transition to -RA from SW to NE overnight.
This trend continues even at KALO for the daytime hours on
Tuesday. Low CIGS and -RA will persist through the day however.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 PM this evening to 8 AM CST
Tuesday for IAZ007-017-026>028-037>039-050.
&&
$$
DISCUSSION...Ansorge
AVIATION...Hahn
Area Forecast Discussion
National Weather Service Grand Forks ND
839 PM CST Mon Nov 23 2020
.UPDATE...
Issued at 839 PM CST Mon Nov 23 2020
Surface temperatures in southeast North Dakota remain quite mild
early this evening. The increasing low clouds in that area and
steady southeast winds will likely keep temperatures steady or
slightly rising overnight. Went ahead and blended in the latest
HRRR temperature guidance for all areas overnight, which has the
same idea of steady or slowly rising temperatures. Looking at some
of the road temperature forecasts, portions of east central and
southeast North Dakota stay above freezing overnight. Therefore,
thinking if any drizzle forms, it would only be freezing north of
highway 200 in North Dakota and across most of the northwest
quarter of Minnesota.
UPDATE Issued at 615 PM CST Mon Nov 23 2020
Low clouds are poised over eastern South Dakota and southwest
Minnesota, and they have been creeping into the far southern Red
River Valley. Temperatures are pretty mild under this band of
clouds, and have yet to see any stations reporting anything
falling out of them. Models are still indicating the potential for
some light precipitation (rain/freezing rain/snow) as these low
clouds work northward late tonight into Tuesday morning. At this
point, see no reason to play too much with the forecast.
&&
.SHORT TERM...(This evening through Tuesday night)
Issued at 343 PM CST Mon Nov 23 2020
Fair skies and breezy southeast winds will persist through the
remainder of the afternoon and evening, with overnight low
temperatures slowly settling into the 20s overall, but staying
nearer the thaw point along the SD border area and into west
central MN.
At the surface, and inverted trof will build into the area as a
low pressure system, now in far northeastern CO, steadily pushes
up into the northern plains region. The main arc of precipitation
from this storm system will spread across southeastern SD and
southern MN through the day on Tuesday, while the inverted trof
anchors into northwestern MN and pulls some moisture and energy
to the area. Expect increasing clouds during the overnight period
with areas of light freezing mist or drizzle developing from
southeastern ND into westcentral and northwest MN throughout the
early morning on Tuesday. Gusty southeast winds will persist
through he morning at from 10 to 20 mph, but turn from the south
by midday, and eventually turn from the northwest through the
afternoon. Daytime highs should rise into the lower to mid 30s
across the northern tier, and reach the upper 30s to around 40
degrees in the southern Valley. Precipitation amounts should range
from trace amounts into a few hundredths of an inch of freezing
drizzle and rain, with a slight amount of snowfall possible along
and north of Highway 2, mainly in northwest MN.
This system should progress steadily eastward through the day,
with clearing skies moving in from the west, behind a cold front,
through the late afternoon and early evening. Seasonably cool and
dry conditions are expected Tuesday night into Wednesday.
.LONG TERM...(Wednesday through Monday)
Issued at 343 PM CST Mon Nov 23 2020
Overview...
Clouds linger into Wednesday morning as a trough moves east of the
Northern Plains into the Great Lakes region. General trend of quiet
weather ensues across the forecast area during the end of the week
and into the weekend. Some areas in the western portion of our
region could see several occurrences of windy afternoons. No impacts
are expected to the region.
Wednesday through Thursday...
Clouds linger through Wednesday morning, with a gradual clearing by
the afternoon as a ridge builds into the Northern Plains. There
exists the potential for some gusty winds Wednesday and Thursday
across portions of the northwestern forecast area. Soundings
indicate some inverted "v" structure in the lower levels and slight
mixing from the 850mb height. Winds have the potential to gust
toward 25-30mph in the Devils Lake region.
Other than some wind potential impact is little to none across the
forecast area, with temperatures remaining seasonal as highs hit the
low 30s toward Fargo. Thursday is slightly warmer with mid 30s north
and low 40s in the south under mostly sunny skies.
Friday and beyond...
A pattern of quiet weather continues throughout the weekend into the
early part of next week, with above normal temperatures to start the
weekend and a return to normal by the end. A low pressure system
moves north of the region across Manitoba during Friday into
Saturday, with a slight possibility of the trailing cold front
bringing flurries to the northern portions of the forecast area.
Models are in disagreement in the amount of moisture available and
the exact track of the system in Manitoba. The trailing cold front
on Saturday brings our temperatures back to seasonal averages for
the end of the weekend and into the first week of December. Pressure
gradients tighten from the passage of the cold front, increasing
winds across the forecast area.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 615 PM CST Mon Nov 23 2020
Lots of things to watch in the aviation forecast. Low clouds are
expected to stream northward tonight, bringing most TAFs into IFR
conditions. Unless fog forms, do not think visibilities will get
restricted. Winds will stay fairly steady, switch to the south
Tuesday morning, then switch to the west by Tuesday afternoon.
Finally, there may be some light rain/freezing rain/snow overnight
into Tuesday morning. Confidence not too high on timing or what
type of precipitation it may be. Will be watching what happens
further southward to get an idea of what may occur.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$
UPDATE...Godon
SHORT TERM...Gust
LONG TERM...Spender
AVIATION...Godon
Area Forecast Discussion
National Weather Service Goodland KS
756 PM MST Mon Nov 23 2020
.UPDATE...
Issued at 755 PM MST Mon Nov 23 2020
Updated precipitation chances slightly for Tuesday morning and
afternoon. Precipitation chances are expected to increase in the
northwestern part of the area Tuesday morning, with a second area of
chances increasing in the southeastern part of hte forecast area in
the afternoon. As temperatures rise, there may be a brief period of
light freezing rain in eastern Colorado.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 1254 PM MST Mon Nov 23 2020
19Z Water vapor imagery and RAP analysis indicated strong short wave
trough approaching the four corners area. This system will be the
primary driver of tonight through Tuesday`s potential precipitation.
At the surface, strong sfc trough deepened across eastern Colorado
as much of the area was covered by thick clouds. Strong southerly
flow was noted across the southeastern portion of the area where
winds were gusting in excess of 40 mph in some locations.
Main forecast concern will be precipitation and potential for winter
weather impacts through the evening Tuesday.
Lots of uncertainty with respect to how this system will evolve and
the first major change to going forecast is to slow precipitation
onset down by 3-6 hours. Despite some elevated instability, bulk of
short term models support a very dry layer of air persisting through
much of the overnight period, especially to the north of cold front.
While it is possible that this level could saturate earlier and lead
to precipitation, think overall pattern supports a slower
evolution/development for precipitation given the overall moisture
profile.
While there is pretty good agreement with overall system evolution
and timing, the presence of elevated instability increases
uncertainty with respect to amounts and may create a situation with
spotty higher amounts surrounded by relatively little precip.
Current thought with respect to precipitation evolution have me
leaning towards seeing two distinct areas of precipitation
initially. The first will be across northeast Colorado along
strong frontogenetic circulation. Synoptic scale support stronger
south and west so think best response will be just to the west of
the forecast area. A second area will develop near the surface
front as saturated low level airmass may support some weak
instability, with a thunderstorm not out of the question during
the morning and early afternoon hours. As H5 trough nears the
area, expect northern area to shift south and gradually
consolidate with precipitation area across southern CWA. Right
now, think this area will diminish as it moves south so there may
be an area that receives relatively little precipitation through
the day. With up to 500 j/kg of mucape available, could see areas
with more significant rain and even convective driven snow, but
these should be very isolated with threat for heavier snow or
precipitation small. Think the biggest potential impact for snow
will be between Burlington and Limon between 12 and 21 UTC, where
1 to 3 inches of total accumulation possible. Given overall poor
snow growth profiles and uncertainty with precipitation placement,
do not anticipate any highlights for snow at this moment.
Precipitation should come to and end quickly after 00z as trough
axis moves well to the east of the area and strong downward motion
will overspread the area. As skies clear and winds relax, expect a
chilly night with lows approaching the teens in some areas.
.LONG TERM...(Wednesday through Sunday)
Issued at 113 PM MST Mon Nov 23 2020
Wednesday... An upper level ridge is expected to move over the High
Plains beginning Wednesday morning bringing dry conditions to the
Tri-State area. Guidance is in good agreement that the ridge will
move quickly across the Plains throughout the day as our next trough
system pushes across the western CONUS. Late Wednesday night, the
upper level winds will shift to the SW as the trough digs into the
Southwest region. At the surface a trough will develop over eastern
Colorado during the afternoon hours, forming a closed low across the
TX-OK panhandles and western Kansas overnight. Temperatures on
Wednesday are forecasted to reach the low to middle 50s for highs
and drop into the low to middle 20s for overnight lows.
Thursday... The Tri-State area will continue to experience SW flow
aloft through Friday as the positively-tilted upper level trough
continues to move east. A cold front is expected to move across the
area Thursday morning from the northwest. The timing of the front is
earlier compared to the previous forecast, but the timing could
still change over the next few days. If the front follows the
current guidance, high temperatures could be cooler than currently
expected. As mentioned in the previous discussion, there is little
moisture associated with this front. The surface low and trough that
formed south of the area Wednesday night is currently expected to
continue east along the Kansas-Oklahoma border. As the low moves
east, the models are showing an increase in moisture over the
eastern half of the CWA Thursday afternoon. Despite the added
moisture, the area should remain dry. The high temperatures are
expected to range from the 40s to low 50s, with cooler temperatures
possible depending on the cold front. Low temperatures are expected
to fall back into the upper teens to mid 20s overnight.
Friday... This is where it gets messy with the models. Both the GFS
and the ECMWF are continuing to depict the trough finally moving
over the CWA throughout the day on Friday. However, the ECMWF has a
different solution with the formation of a closed low over the Four
Corners region at the base of the deep trough. At the surface, high
pressure is expected to move over the Central Plains, keeping the
region dry through the early afternoon. During the late afternoon
and evening hours, chances are currently expected to increase,
mainly south of US-40, for a light rain/snow mix that becomes light
snow as temperatures drop. Little to no accumulations are expected
at this time. Temperatures on Friday are currently expected to range
from the 40s to low 50s for highs and low 20s for lows.
Saturday and Sunday... The models continue to disagree on the upper
level pattern and the location of the trough. The GFS has the trough
moving SE out of the area Saturday morning, followed by a ridge with
surface high pressure. The ECMWF has the closed low just SW of the
area near the CO-NM-TX-OK border. The ECMWF keeps the low stationary
in that general area through the end of the extended period. With
the models differing on the location of the trough, there is also
disagreement on precipitation this weekend. The GFS keeps the area
dry through the end of the period, while the ECMWF keeps
precipitation mainly south of the CWA from Saturday morning through
late Sunday morning. There is a window during the overnight hours
Saturday into early Sunday where areas south of I-70 could see some
precipitation. Due to the uncertainty with the models, the
confidence in any precipitation occurring is low. For now, sticking
to less than 25% for PoPs. There is a slight chance for light snow
across much of the area early Saturday. As temperatures slowly climb
with daytime heating Saturday, the snow could transition to a light
rain/snow mix before becoming completely rain in the afternoon. We
could see another transition from rain to snow during the evening
hours through Sunday morning as temperatures drop and another cold
front passes through the area. Precipitation chances should decrease
throughout the morning from west to east before exiting the area
completely around mid-day. High temperatures on Saturday will be in
the 50s, with lows in the 20s. Sunday will be colder due to the
frontal passage, with highs only in the low to mid 40s. Low
temperatures are expected to range from the mid teens to low 20s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 434 PM MST Mon Nov 23 2020
VFR to IFR conditions forecast for the TAFs. Conditions for KMCK
are expected to deteriorate over the next hour as MVFR ceiling
from the southeast moves in. There may be an hour or two window
during the evening when the ceiling improves to VFR, however
confidence of that occurring is too low to put in the TAF.
Otherwise IFR conditions will move in around 8z for KMCK, with
MVFR conditions for KGLD. These MVFR conditions may be short
lived, and quickly fall to IFR for KGLD. These conditions will
persist into the morning before beginning to improve to MVFR.
Conditions will improve to MVFR when the precipitation begins.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
UPDATE...AW
SHORT TERM...JRM
LONG TERM...KMK
AVIATION...JTL
Area Forecast Discussion
National Weather Service Wichita KS
556 PM CST Mon Nov 23 2020
.SHORT TERM...(This evening through Wednesday night)
Issued at 419 PM CST Mon Nov 23 2020
Highlights:
1) Drizzle tonight changing to showers Tuesday
2) Thunderstorms Tuesday evening in southern KS - strong to severe
possible
3) Rain/snow mix or snow possible in north central KS Tuesday night
4) Temps in upper 50s Tuesday and low 50s Wednesday
Challenges:
1) Temperatures on Tuesday
2) Timing of post frontal cold air on Tuesday
Changes:
1) Increased/modified precipitation chances
2) Increased precip chances Tuesday afternoon with quicker exit
As moisture transport continues to increase through Tuesday, this
will help saturate the low levels. Anomalies for precipitable water
values indicate the same two to four standard deviations above
normal from this evening into Tuesday evening. Model soundings
indicate drizzle will be possible tonight before complete saturation
of the column occurs late tonight into early Tuesday. At that time,
there will be larger droplets with a change to showers and
increasing chances for precipitation around daybreak and through the
day. The previous discussion pointed out a similar challenge of the
daytime temperatures given the cloud cover and precipitation but an
aid of low level warm air advection; forecast high temperatures fit
with the general consensus of most models albeit just a tad higher
with minimal changes from the previous forecast.
The trough over Great Basin maintains its eastward trajectory and is
still on target to move through on Tuesday. This is the most
notable system within the forecast as the path is directly east
across Kansas. As the system moves into the Plains, it closes off
or essentially strengthens. The forcing associated with this low
combined with the instability/shear should result in thunderstorms
as has been noted for the last several days. There is some
surface instability (~500 J/kg) at its peak unless you believe the
RAP which has values closer to 1k J/kg. Shear appears to the
greater indicator with roughly 40-60kts on hand. The focus for the
convection appears closely tied to the front and its respective
passage which would put a peak time in the early evening hours
(~0Z or 6PM) for south central Kansas. As the Storm Prediction
Center has indicated in their updated Day 2 Outlook, the potential
area for a few strong to severe thunderstorms will be in southern
Kansas with the better potential in Oklahoma based on the
addition of a slight risk. Bulk shear vectors are nearly parallel
to the cold front which would suggest convection to be more linear
in nature. In Kansas, the threats are nickel to quarter sized
hail and 50-60 mph winds.
As cold air is ushered behind the front, this could result in a mix
of rain/snow or snow across north central and northwest Kansas
Tuesday night into early Wednesday. Drier air moves into the mid
levels during this time which would limit the window for a mix or
snow. On the other hand, a quicker arrival of colder air would
increase the longevity for snow and potential accumulation given the
steep lapse rates/lift as the last discussion mentioned. Surface
soil temperatures are still in the 40s which would help. Given the
current expectations, minimal if any accumulation is anticipated at
this time. Any minimal accumulations would not last long given those
temperatures and air temperatures above freezing Wednesday morning.
The system will push east and northeast to the middle Mississippi
River Valley by mid day Wednesday. Therefore precipitation should
end by Wednesday morning before sunrise. Clouds should clear out
through the day, and high temperatures should be about seasonal
normal in the lower 50s.
.LONG TERM...(Thursday through Monday)
Issued at 419 PM CST Mon Nov 23 2020
Highlights:
1) Thanksgiving forecast: Temps - low 50s to near 60. No precip
2) Slight chances of precipitation in southern KS Fri eve-Saturday
3) Temperatures in the upper 40s to mid 50s Friday to Sunday
Thanksgiving forecast: Overall it will be a fairly nice day. High
temperatures are forecast in the lower 50s in north central Kansas
to around 60 along the Kansas/Oklahoma border. This will be near or
above the climatological normal values. No precipitation is
expected. Scattered clouds will be combined with winds at 10 to 15
mph. Thus it will be a good day to talk a walk or do some other
outdoor activity before or after your meal.
A weak wave is progged to move through on Friday with slight precip
chances moving in Friday night. There is no change in the differing
model solutions. The ECMWF shows a quicker to deepen solution
closing off its low near the Desert Southwest while the GFS is the
slower solution and further to the south. Both models indicate a
southeast track and keeping the main system to the south. Given this
variability, the slight chances seem to be representative for now.
Cool air advection may move in Sunday to cool down the start of next
week with high temperatures down to the mid 40s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 555 PM CST Mon Nov 23 2020
Main concerns: LLWS overnight, IFR/LIFR flight conditions across
the area, and northerly wind shift in central KS toward the end
of the TAF period.
Marginal LLWS possible at most sites overnight, though breezy sfc
winds will likely limit LLWS at times. Ceilings will continue to
drop overnight area as strong moisture advection is ushered in.
Expect widespread IFR conditions and periods of LIFR conditions,
except at KCNU which should be delayed and remain near MVFR through
late tomorrow morning. Winds will remain out of the south until the
cold front arrives tomorrow afternoon. The northerly wind shift
should arrive in central KS in the 18-21Z timeframe tomorrow.
Precipitation wise- Periods of light drizzle will be possible
overnight which could temporarily reduce vis, but left out of TAF
for now given scattered nature. Thinking remains that the area
will remain mixed enough to not develop much, if any, fog.
Expect scattered showers and storms tomorrow along and ahead of the
cold front. A few storms tomorrow late afternoon to early evening
could be strong to severe with nickel to quarter size hail and wind
gusts to 60mph.
&&
.PRELIMINARY POINT TEMPS/POPS...
Wichita-KICT 47 58 35 51 / 50 80 70 0
Hutchinson 47 58 33 51 / 50 80 70 0
Newton 46 56 34 50 / 50 80 80 10
ElDorado 47 57 36 50 / 60 80 90 10
Winfield-KWLD 48 58 36 53 / 60 80 70 0
Russell 46 57 29 49 / 40 80 60 0
Great Bend 46 58 30 50 / 40 80 60 0
Salina 46 57 33 49 / 50 90 90 10
McPherson 46 57 32 49 / 50 80 80 10
Coffeyville 47 58 40 54 / 50 80 90 10
Chanute 47 56 40 51 / 50 80 90 10
Iola 46 56 39 51 / 50 80 90 10
Parsons-KPPF 47 57 41 52 / 50 80 90 10
&&
.ICT WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...VJP
LONG TERM...VJP
AVIATION...KMB
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
905 PM CST Mon Nov 23 2020
.UPDATE...
905 PM CST
The overall forecast looks on track this evening. 00Z ILX/DVN
RAOBs and recent MDW AMDAR soundings reveal a substantial amount
of dry air in the 750-900 hPa layer across northern Illinois. This
instills some concern of the behavior of the initial precip band
at the surface, with the potential for pockets of heavier precip
instead of a solid line shifting northeast across the area during
the overnight hours. With that said, latest hi-res guidance still
supports moderately to briefly heavy snowfall rates for a 1-2
hour period at onset with the initial band. Have therefore opted
to make very little change other than to tighten the PoP gradient
on the northeast side of the precip band through daybreak
Tuesday. Additionally, have moved up the start time of the
advisory for Ogle and Lee counties to midnight as moderate to
briefly heavy snow may be ongoing as early as around 1 am.
Kluber
&&
.SHORT TERM...
310 PM CST
Through Tuesday night...
The first Winter Weather Advisory of the season has been issued
for parts of the far west and northwest Chicago suburbs, out to
north central and northwest Illinois portion of the CWA. Advisory
was issued in collaboration with WFO DVN and MKX to emphasize
impacts to travel during the morning commute, including
slick/slushy spots on some roads and visibility as low as ~1/2
mile at times. Most of the CWA except parts of the far south
should have a period of all snow as precipitation type and low
visibility from this event. However, with more marginal >32F
surface temps and overall lower snow totals forecast, impacts
should be mitigated.
A potent mid/upper level impulse over the Great Basin region will
be the primary driver of the weather system set to impact our
local weather through Wednesday. A developing surface low across
the front range of the Rockies is occurring in response to the
mid/upper level short-wave digging into the Four Corners region of
the southwest CONUS. The associated downstream southerly low-
level mass response will drive a southerly 50+ kt low-level jet
from the Plains east-northeastward into the Upper Midwest tonight
into Tuesday, resulting in a rapidly northward shifting plume of
deep Gulf Moisture into the region. This will set the stage for
rapid precipitation development into the area later tonight,
despite antecedent very dry air aloft.
The area of precipitation will blossom and/or expand northward
across the CWA overnight as warm advection and isentropic ascent
become quite robust. As alluded to in intro, precipitation type is
expected to be mainly in the form of snow for most of the area for
at least a few hours after midnight through the early morning.
With baroclinic zone oriented from northwest to southeast and
continued strengthening warm advection will gradually transition
p-type to rain from southwest to northeast. The warming aloft will
gradually offset dynamic cooling processes along with an easing of
forcing as a lead positive tilt wave shifts northeast of the area.
While it can`t be ruled out that some sleet may briefly mix in
during the transition, the increasing southeast surface winds
should lead the surface temps to rise safely above freezing as the
>0C air aloft rushes in. Thus, think that p-type transition for
most locations will be one of snow to rain.
While the window for steady snow with this system will generally
only be for about 3 to 6 hours for most locations, there is
increasing concern that the rates could be moderate, to even
briefly heavy into early Tuesday morning, thus accumulations
appear likely for many areas of northern IL inland from the lake,
and this would impact the Tuesday morning commute. Forecast
soundings, especially from the NAM/WRF guidance and RAP have an
approximate 2-4 hour window of good co-location of very strong
omega through the DGZ, which is a favorable look for moderate to
briefly heavy snowfall rates.
Looking more in depth, model guidance continues to suggest that a
stout, but transient band of 700-500 MB frontogenesis will
develop northward into the area very late tonight into early
Tuesday morning. The associated ageostrophic response should force
good ascent right through the favored dendritic growth zone, as
noted above. This in combination with very steep lapse rates
through this layer from around 600 mb through 400 mb suggest that
the snow may fall at a heavy rate for a couple hour period early
Tuesday morning. There is even support for larger snow flakes due
to aggregation processes in the lower-levels, resulting from a
deep moist isothermal layer just below 0C from the surface to just
above 700 mb. This could thus support accumulations on some area
roads, in spite of marginal surface temperatures, so impacts to
the Tuesday morning commute look probable, especially outside the
main urban center of Chicago. Exact response of road temps to
heavier snow rates is uncertain, but with signal for strong
dynamic cooling evident, think that surface temps will be kept
around 32F. This should enable for slushy accums on some roads,
especially lesser traveled secondary roads and bridges.
Total snow accumulations look to be in the 1-3" range I-80 and
north in Illinois and roughly along/west of I-294, with little/no
accumulation along the lakefront in Chicago. Can`t rule out some
isolated >3" amounts closer to the Wisconsin border within
advisory area where change to rain will be the latest. Any
accumulation in the city stands to predominantly be on grassy/colder
surfaces and main travel impact would be from the lower visibility.
Speaking of visibility, favorable factors listed above will also
be favorable for periods of visibility below 1 mile during the
heaviest snow, possibly as low as 1/2 mile at times. All in all,
with the greater impacts to the commute likely focused into
interior northern Illinois, opted to issue the Winter Weather
Advisory for McHenry, Kane, DeKalb, Winnebago, Boone, Lee, and
Ogle Counties, in effect from 2AM to 10AM.
After the transition to rain clears the entire area to the north,
there will be continued periods of rain of varying intensity
through Tuesday night. As the surface low pressure area moves
closer after midnight Tuesday night, temperatures in the lower to
mid 40s and similar dew points (little/minimal T/Td spread) will
mean saturated low levels and a chance for fog development.
Especially where rain rates become light coupled with lighter
winds, will have to monitor the potential for patchy dense fog in
spots. There was a signal for this on some of the MOS guidance in
parts of northern Illinois.
Castro/KJB
&&
.LONG TERM...
158 PM CST
Wednesday through Monday...
Extended forecast highlights include mid-week rain, quiet and
relatively mild weather for the Thanksgiving holiday into the
weekend, then a low-confidence but potentially unsettled period
Sunday into Monday with a push of colder air early next week.
Guidance remains in good agreement in depicting a closed upper
level low near Kansas City early Wednesday, nearly stacked atop
its associated occluded surface low. Low level southerly winds
ahead of this circulation will continue to advect Gulf moisture
into the region during the day, maintaining rain/shower threat as
the low tracks northeast across the southeastern part of the WFO
LOT cwa by late afternoon. A couple of areas of better focus for
precipitation and higher rainfall amounts are noted, one across
our southeastern counties where unseasonably mild/moist (temps in
the mid-upper 50s and surface dew points around 50) in the
vicinity of the triple point of the occlusion will reside, and a
second farther north across northwest and far northern IL where
better baroclinicity exists along an inverted cold frontal trough
north/northeast of the low. Forecast soundings continue to depict
some weak MUCAPE across our southern counties Wednesday afternoon
near the triple point, worthy of at least some slight chance
thunder mention there. Rain should taper off and end from west to
east Wednesday evening as the upper trough and surface low move
off to the east of the forecast area.
Weak surface high pressure ridge moves in behind the departing
system late Wednesday night into Thanksgiving day, though given
the occluded nature of the departing low there is not much of a
push of cooler air, and no deep/strong subsidence to erode
lingering low level cloud cover. It will be dry and relatively
mild for the holiday however, with high temps around 50 degrees
expected. Quiet weather looks to persist through the end of the
week and into at least the first half of the weekend, as large
scale upper trough becomes positively-tilted across central and
western North America. Similarly dry and relatively mild
conditions appear in store for the region again Friday and
Saturday.
Models have shown some significant differences with the evolution
of the upper pattern later in the weekend into early next week.
Guidance is in generally good agreement in closing/cutting off an
upper low across the southwestern CONUS by the weekend, while the
northern portion of the aforementioned upper trough progresses
eastward with a dry pacific cold frontal passage across our area
Friday. Previous runs of the ECMWF and GEM then depicted another
upper trough phasing with the southern closed low and developing a
strongly amplifying upper trough and deep low surface low which
would affect the Midwest Sunday-Monday. 12Z runs of these models
have trended toward the GFS solution of a somewhat more
progressive southern stream low and no phasing/impressive
amplification of a deeper trough across the Midwest. Getting a
look at 12Z ECMWF ensemble mean does still spread some lighter
precip across especially our south/southeastern cwa Sunday/Sunday
night, so am a bit hesitant to pull pops completely during that
period so will maintain some slights/low chance focused on
Sunday/Sunday evening. Could be some rain/snow mix in colder
evening hours, though mainly rain expected with temps well above
freezing (40s) during the day.
Ratzer
&&
.AVIATION...
For the 00Z TAFs...
548 PM...Forecast concerns include...
A period of moderate snow predawn hours thru mid morning.
Rain showers for the rest of the period.
Ifr cigs Tuesday morning...lifting to low mvfr in the afternoon.
Gusty southeast winds Tuesday.
An area of snow currently over southern IA and northern MO will
continue moving northeast and will reach the terminals in the
predawn hours. Current timing in the tafs looks on track. Vis/
cigs should quickly drop into ifr as the snow begins. There may be
a 1-2 hour period of vis in the 1/2sm range along with lifr cigs.
As the precip intensity begins to diminish by mid morning...the
precipitation will mix with then change to light rain. Medium
confidence on this timing. Ifr cigs are expected to lift to low
mvfr for the Chicago terminals...but ifr will be nearby to the
northwest. Ifr cigs are possible at ord/dpa...at least for a time
Tuesday afternoon. Rain showers will continue Tuesday afternoon
into Tuesday night. Eventually cigs will lower back to ifr Tuesday
evening.
Easterly winds will turn southeast later tonight with speeds
increasing to 10-12kts. Winds will remain southeast Tuesday with
some gusts into the 20kt range. Winds will slowly turn more
southerly Tuesday evening. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory...ILZ008-ILZ010...midnight Tuesday to 10
AM Tuesday.
Winter Weather Advisory...ILZ003-ILZ004-ILZ005-ILZ011-ILZ012...2
AM Tuesday to 10 AM Tuesday.
IN...None.
LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...9 AM Tuesday to 6 AM Wednesday.
&&
$$
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Area Forecast Discussion
National Weather Service Miami FL
811 PM EST Mon Nov 23 2020
.Update...
Generally quiet conditions across South Florida in the short-term,
as a weak surface front continues to move southward through the
remainder of our area. Along and behind this boundary, isolated
showers continue to develop over the Atlantic waters off South
Florida, where marginal surface-based instability remains in place
(owing to lingering dewpoints in the upper 60s F and moisture fluxes
atop the Gulf Stream). In addition, 40 knots of mid-level flow is
supporting enhanced bulk shear over the Atlantic waters, which has
allowed for periodic organization (mid-level rotation) within some
of the above mentioned convective showers. The primary concern with
this activity has been waterspout potential and brief gusty winds,
though the latest RAP mesoscale analysis and 00Z MFL RAOB suggest
that the instability is becoming elevated, which will limit the
overall waterspout risk with time. As the surface front continues
southward, dry air will continue to filter into South Florida, as
a mid-level high builds over the eastern Gulf of Mexico. This
combination should support strong subsidence and an associated
warm/dry layer aloft -- suppressing most convective development
during the day on Tuesday.
Winds will continue to transition from a northerly direction to an
east-northeasterly direction while the pressure gradient tightens
behind the above mentioned surface front. The onshore flow component
and enhanced pressure gradient will support breezy conditions
tomorrow, especially along the east coast of South Florida. This
will also support a lingering elevated rip current risk along the
east coast beaches. Temperatures will remain near-normal or
slightly below average (mainly inland/SW FL), while dewpoints in
the 60s F tomorrow should support a fairly comfortable day.
&&
.Prev Discussion... /issued 702 PM EST Mon Nov 23 2020/
Aviation (00Z TAFs)...
Primarily VFR through the period, though isolated SHRA could
linger along the east coast of S FL overnight. Any impacts from
this activity should be limited. NNW flow will will continue to
transition to NNE, becoming breezy during the day tomorrow.
Prev Discussion... /issued 342 PM EST Mon Nov 23 2020/
Short Term...
Today
Drier air advecting over the region today, as a 500 hPa ridge of
high pressure progresses over the Florida panhandle. The eastern
periphery of this ridge will induce cold air advection over the
region, further supported by pressure rising at the surface.
Isolated showers will be generally confined over the Atlantic waters
and along the coast, with 15-20 PoPs over the aforementioned areas.
Meaningful accumulations are not anticipated with any developing
showers. Rain chances will decrease further Tuesday with a surface
trough moves through the region, as dry conditions are anticipated
over South Florida.
Maximum temperatures are forecast to be seasonably cooler, with
upper 70s/lower 80s across the region. With a low-level trough
forecast to progress over the region Monday night/Tuesday morning, a
north/northeasterly wind will cause a drop-off in dewpoints
temperatures and hence a slight decrease in apparent temperatures as
well.
Long Term...
.Tuesday Night through Sunday...
Benign, dry, and seasonal conditions will continue to prevail across
South Florida for the remainder of this week, as a ridge of high
pressure aloft becomes established over our area. The weak frontal
boundary that traversed across our area earlier today will continue
to drift towards the south and will dissipate over the Florida
Straits as airmass modification continues to occur to the north of
the boundary. With high pressure in firm control this week, model
consensus continues to keep a cold front well to the north of our
area. As the high slides eastward during this week, upper-level
zonal flow across the region will be of westerly orientation. At the
surface, easterly winds will prevail. As precipitable waters
values during the first part of this week are within the 1.0 to
1.4 inches range, isolated showers along the adjacent Atlantic
waters and the east coast of South Florida cannot be ruled out.
During the remainder of this week, high temperatures will continue
to be in the low 80s across our area with overnight temperatures
in the upper 60s to the low 70s.
.Sunday Night through Monday...
While there is considerable uncertainty in long-term model
guidance, current indications point to the approach of a strong
cold front towards our area early next week. With the potential
passage of this strong cold front across our area, this portion of
the forecast period will be important to monitor for potential
weather impacts and changes in forecast. The timing and strength
of the cold front will dictate the potential low and high
temperatures during this portion of the forecast period.
Marine...
A surface trough will progress through the Atlantic and Gulf waters
today. Winds are forecast to change direction from northerly to
northeasterly across the local waters as the front continues to move
southward. A Small Craft Advisory is in effect for the offshore
Atlantic waters through at least Tuesday. This advisory could expand
towards the nearshore waters and may require an extension beyond
Tuesday depending on how conditions evolve with time.
Beach Forecast...
With decreasing easterly flow, rip currents become less favorable
today. However with the wind direction shifting from north to
northeast with a passing surface trough, a moderate risk for rip
currents will remain through at least Tuesday for the Atlantic
beaches.
&&
.Preliminary Point Temps/PoPs...
West Palm Beach 70 79 69 80 / 10 10 0 0
Fort Lauderdale 71 81 72 81 / 20 20 0 0
Miami 70 81 71 82 / 20 20 20 0
Naples 64 84 66 83 / 0 0 0 0
&&
.MFL WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...Small Craft Advisory until 7 PM EST Tuesday for AMZ670-671.
GM...None.
&&
Update...18/Weinman
Aviation...18/Weinman
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
621 PM CST Mon Nov 23 2020
.UPDATED for 00Z Aviation Discussion...
Issued at 617 PM CST Mon Nov 23 2020
&&
.SHORT TERM...(This evening through Tuesday night)
Issued at 254 PM CST Mon Nov 23 2020
Weak high pressure atop the region, responsible for the plentiful
sunshine experienced across the region today, will slide off to the
east with a potent but compact low pressure center on its heels. This
system will be kicked northeast from the lee of the Central Rockies
with the help of a digging and merging trough moving away from the
western CONUS coast and across the Rockies today into tonight. The
low pressure center will shift east over the Central Plains tonight
and into the mid-Mississippi River Valley by Tuesday evening, owing
to the southern jet stream. Complicating this surface low will be an
additional cold front sagging south from a south- central Canadian
low pressure center, which is being activated by the northern jet
stream. The split jet will essentially merge over the Midwest tonight
into tomorrow, which will expand the precipitation shield across the
area tonight through Tuesday. P-type has been the most complicated
factor over the past few days with this event, but the overall trend
has been to slightly nudge up temperatures little by little each day
and model run, culminating in a greater-than-50th percentile forecast
in the low temperatures tonight. Also, in addition to the moisture
surge accompanying this system will be modest warm air advection in
the boundary layer, resulting in a more rain-like p-type pattern for
much of the event as it drags on through tomorrow. Thus, the key part
is the p-type in the early hours of the event. The SREF and HRRR
have been keying in on a wintry mix of freezing rain/snow for west-
central into north- central MN with this event, particularly after
midnight through midday Tuesday. Model soundings are also indicating
a slight enough warm layer off the deck to produce a few hours of
potentially prevailing freezing rain for a handful of counties in the
northern tier of the WFO MPX coverage area. With a few hundredths of
an inch of icing likely, have opted to run with a small winter
weather advisory in that portion of the area. South of there, a
mainly rain/snow event will unfold but with again lower snow amounts
than the previous forecast due to the greater influx of warmer air.
Still, up to 1" snow accumulation may develop for the eastern half of
the coverage area overnight into Tuesday morning. The p-type will
steadily change over to all rain as the day progresses, with the
precipitation gradually waning from west to east Tuesday afternoon
and evening. A few lingering rain showers are then possible for far
eastern and southern portions of the coverage area going into Tuesday
night but the vast majority of the coverage area will simply have
mostly cloudy skies Tuesday night.
After lows tonight drop to the mid 20s in northern and eastern
portions of the coverage area and lower 30s in western and southern
portions, highs will generally range 35-40 degrees on Tuesday. Could
potentially be a couple degrees cooler should some evaporative
cooling effects take place, which could nudge up snow amounts by a
couple-few tenths of an inch. As the precip ends and the frontal
system moves across and departs the area Tuesday night, lows will
range from the mid 20s in western MN to the lower 30s in southern MN
and western WI.
.LONG TERM...(Wednesday through Monday)
Issued at 254 PM CST Mon Nov 23 2020
Any lingering light rain or snow showers from left over from the
departing storm system will end Wednesday morning. This will set up
a relatively quiet period with little to no additional precipitation
and temperatures running above normal for late November.
Upper level split flow will dominate through the forecast period.
Several moisture-starved shortwaves will move through the Upper
Midwest. As a result, frontal passages will remain dry and mild air
will return behind the exiting troughs. The biggest change from last
nights forecast guidance is the shift on the 12z ECMWF and
Canadian models. 00z solutions had an amplified trough and jet
phasing between the northern and southern streams. This resulted in a
storm system that tracked into the Great Lakes keeping the MPX CWA
in the cold sector. The 12z solutions now favor the continuation of
split flow with no phasing with a closed low over the southern CONUS
and a dry frontal passage on Sunday across the upper Great Lakes.
Thus, the period will remain dry and mild through the weekend with a
potential cooldown for the end of November.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 617 PM CST Mon Nov 23 2020
VFR conditions at the start of the period will give way to MVFR/IFR
conditions overnight as a surge of moisture lifts northward. This
will bring wintry precipitation across the region, as well as IFR and
possibly LIFR ceilings. Winds will be primarily out of the southeast,
but eventually become northwest Tuesday evening and overnight.
KMSP...
Did speed up the start time of the MVFR/IFR conditions as the
moisture surge seems to be ahead of schedule. There is a chance for
some freezing drizzle, but this looks like more of a snow/rain event
for KMSP. Expect IFR conditions for most of the day at KMSP.
/OUTLOOK FOR KMSP/
Wed...Lingering MVFR clouds early, then VFR. Wind SW 5-10 kts
becoming NW.
Thu...VFR. Wind SW 10 kts.
Fri...VFR. Wind W 10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Winter Weather Advisory from 4 AM to 10 AM CST Tuesday for Benton-
Douglas-Kanabec-Mille Lacs-Morrison-Todd.
WI...None.
&&
$$
SHORT TERM...JPC
LONG TERM...BPH
AVIATION...JRB