Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/22/20
Area Forecast Discussion
National Weather Service Caribou ME
931 PM EST Tue Jan 21 2020
High pressure will slide south of the area overnight. A warm
front will cross the area Wednesday followed by high pressure on
Thursday. A cold front will push into the area Thursday night
and stall over the region on Friday. Low pressure will approach
Saturday and track south of the Gulf of Maine Sunday.
.NEAR TERM /THROUGH WEDNESDAY/...
930 PM Update: This update, we brought in cldnss a little faster
tngt by an hr or two from the prev update and went with a
greater temporal window of sct flurries with both HRRR model
radar ref and obsvd radar ref trends showing more than one ln
of flurries movg across the FA from QB prov. Otherwise, fcst
hrly temps/dwpts updated into the late ngt hrs based on trends
seen from latest sfc obs with only modest reductions of low
temps ovr NW vlys, and this based on perhaps some clrg toward
daybreak, so tngt`s lows do not look to be nearly as cold has
last ngt`s attm.
Prev Disc: A small upper level shortwave sliding southeast into
the area overnight will bring some clouds and a few flurries.
The timing of the shortwave brings some flurries into the
northwestern highlands late this evening, central highlands
around midnight then eastern areas between midnight and dawn. A
very light dusting of snow is possible in some spots with the
best chance for a dusting across central parts of the area. The
shortwave will slide southeast of the region Wednesday morning
as an upper level ridge springs across the area. A return flow
behind surface high pressure to the south will push a warm front
across the region around midday Wednesday. Highs Wednesday will
be near normal for this time of year ranging from the low 20s
north to the upper 20s Downeast. The warm frontal passage will
keep the north mostly cloudy in stratus clouds Wednesday while
Downeast has a partly sunny sky.
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
A period of quiet weather will continue mid to late this week
with moderating temperatures. A warm front will cross the area
Wednesday night, which will keep temperatures significantly
milder compared to the previous couple nights. There may be just
enough moisture along the warm front for some flurries or
perhaps an isolated snow shower across the far north late
Wednesday night into early Thursday morning. Temperatures
Thursday afternoon will be significantly above normal, with
highs above freezing for most. Blended the 75th and 90th
percentiles for max temperatures given 850mb temperatures around
-2C and a greater potential for warmer than forecast
temperatures given the currently mostly cloudy model guidance.
Thursday night will remain mild before a weak cold front with an
unimpressive temperature drop behind it clips northern areas.
Highs on Friday will be slightly cooler, but are expected to
remain above normal.
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Above normal temperatures and quiet conditions will persist
through Saturday as an anomalous upper level ridge remains in
place over much of eastern Canada. A trough undercutting the
aforementioned ridge will close off into an upper level low over
the Mississippi River Valley by Friday evening. The system will
slowly progress across the Mid-Atlantic Saturday before
emerging off of Cape Cod Saturday night into Sunday. There
continues to be modest model agreement regarding the low track
moving due east of Cape Cod, but less confidence on the northern
extent of its precipitation shield. Given the low track,
southern parts of the forecast area will be favored for the most
significant snow accumulations, while far northern Maine will
see lighter accumulations and may even miss snowfall entirely
based on some GFS and Euro ensemble members. The 12z CMC and
Euro also still show a chance for mixing along the coast despite
a favorable low track, which is due to the mild air that will
be in place underneath the aforementioned upper level ridge. Any
remaining snow will end Monday night with ensembles favoring
drier conditions and near normal temperatures for Tuesday.
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Tonight: VFR, possibly briefly lowering to MVFR across the
north late. Light SSW winds.
Wednesday: VFR. Light south wind.
Predominately VFR expected Wednesday night through
Saturday. MVFR ceilings are possible at the Aroostook County
terminals Wednesday night. MVFR to IFR conditions due to snow
are likely across Downeast terminals and possible across
northern terminals Saturday night through Sunday.
Winds will be light tonight and Wednesday. Seas will be 2 ft or
Winds and seas will remain below small craft
advisory levels through Saturday. Gale conditions will be
possible late Saturday night into Sunday.
Area Forecast Discussion
National Weather Service Grand Junction CO
1059 AM MST Tue Jan 21 2020
.SHORT TERM...(Today through Wednesday)
Issued at 250 AM MST Tue Jan 21 2020
Showers have started to develop across the area as the left exit
region of a subtropical jet lifts out of the southwest. Current
temperatures and wet bulbs support snow as the main precipitation
type. These showers may struggle to reach the ground initially,
especially in the valleys, given the low level dry air present as
evident in the GJT 00z sounding. Coverage of the precipitation is
expected to increase this morning as moisture continues to spread in
from the southwest. The shortwave trough will progress eastward over
the area during the day and support weak large scale lift. The 00z
sounding shows and models agree that lapse rates are fairly moist
adiabatic therefore convection might not play much of a role today.
The models depict that a majority of the shortwave energy passes
south of the area so the La Sals, Abajos and San Juans look to be
favored. Although the snowfall rates may struggle to reach an inch
per hour due to limited forcing.
The one thing going for this system is the quality of moisture
advecting across the region. Some of the valleys in southeast Utah
and southwest Colorado could see some snow this morning and through
out the day. As of now there are indications that there is a
potential for a few inches in these areas, but temperatures are
expected to warm above freezing later today. The hope is that the
clouds do not keep daytime warming limited. The main concern is the
corridor from Blanding/Monticello to Durango where the latest HRRR
runs and NAM show 2-4 inches, which seems unlikely. Some other
valleys could receive snow as well, but even the lowest guidance for
temperatures hint at highs reaching at least freezing under the warm
advection. The trough crosses the Divide this evening leaving
westerly flow in it`s wake, which will support orographic lift
through most of the overnight. The orographic snow should focus in
the northern and central mountains.
.LONG TERM...(Wednesday night through Monday)
Issued at 250 AM MST Tue Jan 21 2020
By Wednesday drier air works in from the west ahead of the next
shortwave trough. The main energy associated with this trough will
pass north of the area, but the southern extent looks to clip the
northern and central mountains Wednesday morning. This may cause an
increase in coverage and intensity of the snow in these locations.
With that being said the rates still appear to be rather light and
under one inch per hour especially given the weak forcing. The
shortwave trough quickly progresses eastward and deepens over the
central plains causing the flow to become more northerly. This
should shut down the orographic snow on Thursday that may be
lingering in the northern mountains. Snow amounts still appear to be
below criteria especially with the light rates over the two-day
period. The Park Range could see 6-12 inches, which are the highest
amounts across the forecast area. The Flat Tops and Elks look to be
in the 4-10 range, while the remaining ranges could get 2-6 inches.
Split flow develops this weekend, which will send a ridge over the
region on Friday that gets quickly flattened as yet another wave
moves over the northern Rockies. The models then show several
shortwave troughs coming ashore in the West Coast over the weekend.
This should support a stronger ridge over the region and a warming
trend into Sunday. Models then begin to diverge on how these troughs
evolve, but regardless each solution shows unsettled weather
returning by next week. They generally show a deepening wave that
digs southeastward over the region and potentially becomes closed
off before lifting out over the plains. The associated air mass
would keep temperatures below normal through this period. Prepare
for solutions to change though because this pattern looks pretty
.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1041 AM MST Tue Jan 21 2020
Showers continue to spread from southwest to northeast. Expect
periods with conditions dropping below ILS breakpoints during the
morning hours, with conditions improving overall by mid-
afternoon. However, expect more showery, convective precipitation
to move into eastern Utah and western Colorado this afternoon as
widespread precipitation moves to the east. Frequent mountain
obscuration should be anticipated through the next 24 hours.
Area Forecast Discussion
National Weather Service Key West FL
1023 PM EST Tue Jan 21 2020
Cold northerly wind gusts of 30-35 mph have affected the Florida
Keys this evening. The quickness with which colder air arrived
today helped it to keep its continental polar character. Sunrise
on Wed morning is expected to see the coldest temperatures in 2
years, and possibly even 5 years depending on how cold it gets.
May need to nudge tonight`s forecast low at Key West up a couple
degrees due to the continuing westerly component to the north wind
keeping a longer trajectory across Gulf waters. The latest HRRR
shows a low of 52 degrees. Meanwhile, the forecast of lower 40s in
the Upper Keys is well in line with this evening`s newly arrived
Don`t let the cold north winds tonight fool you. We are still
surrounded by warm, tropical waters. The water temperature is
still 75F at Key West Harbor and 76F at Fowey Rocks just off
Biscayne Bay. Once we lose the cold north winds and they become
northeast, the air mass will modify swiftly.
Is interesting to watch the deepening low center about 100-150
miles east-northeast of the northernmost Bahamas. It will stick
around through Wed but then start to exit eastward on Wed night.
As it exits, our winds will snap northeast, bringing in a more
ocean-modified air mass. Following a day when temperatures will
struggle to reach the 60s over the Keys, they will then struggle
to fall much if any on Wed night. In fact, the warm advection
pattern coming in from the Bahamas could bring a few showers by
late Wed night to the far Upper Keys near Ocean Reef.
Near-gale northwest-north breezes are being observed across the
Keys waters, with occasional gusts near 35 knots at many
observing sites, especially adjacent to the Lower Keys. This is
driving large and steep swell through the Gulf waters. Pulley
Ridge buoy (85 miles north-northwest of Dry Tortugas) is observed
9-foot seas with a dominant period of 7 seconds. As this swell
propagates south-southeast, a more fully arisen sea closer to
12-14 feet should be expected in the Gulf-exposed western Straits.
Meanwhile, northerly gales well offshore the Space and Gold
Coasts will drive 10-12 foot northerly swell into the far eastern
Straits on Wed.
Winds are likely reaching their peak now, but speeds will be slow
to come down much until late Wednesday. So top-end Small Craft
Advisory conditions will continue through the night.
The weather setup is a deepening low pressure center about 100
miles east-northeast of the northernmost Bahamas, with the Keys
getting the near-gale northerlies to its west. The low center will
start to exit eastward on Wed night, with a surface ridge axis then
extending from New England down the U.S. eastern seaboard. This
will cause our winds to snap northeasterly on Wed night, while a
loosening pressure gradient will bring a quicker easing trend.
A light-wind col in the flow should cross the Keys on Friday, then
a less vigorous cold front will slip in from the north on
Main immediate concern is the strong northerly cross-wind
component on the east-west runways at EYW and MTH. Wind gusts near
30 knots are being observed this evening. An ever-so-slow easing
trend will begin overnight and continue through Wed, with little
change in the northerly surface wind direction. By Wed afternoon,
gusts will have come down into the 15-20 knot range.
Strong low-level flow out of the NNW continues to bring a fresh
supply of SCT-BKN cold air strato-cumulus clouds born over the
warm Gulf waters and across the Lower Keys, reaching EYW with
bases near 040. In contrast, the Middle and Upper Keys (including
MTH) are clear due to the over-land wind trajectory. Flow aloft
will start to veer more northerly late tonight, helping to clear
out the Lower Keys toward sunrise.
The last time that the temperature dipped as low as 53 degrees at Key
West International was just over 2 years ago on January 18, 2018.
This means that the temperature in Key West tonight could be the
coldest in over 2 years. The last time that the temperature fell
below 53 degrees was on February 20, 2015, when the low
temperature reached 49 degrees. So it is likely to be the coldest
night in 2 years, and possibly the coldest in 5 years.
GM...Small Craft Advisory for GMZ031>035-042>044-052>055-072>075.
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Area Forecast Discussion
National Weather Service Phoenix AZ
553 PM MST Tue Jan 21 2020
.UPDATE...Updated aviation discussion.
A weather system will exit the region tonight, however residual
moisture in the form of low clouds and fog will linger across parts
of the area into Wednesday afternoon. Skies will eventually clear
and a rapid warming trend will take place during the latter half of
the week. Temperatures over the weekend will be around 5 degrees
above average with just some occasional passing high clouds.
Afternoon WV imagery and objective analysis shows the more
pronounced subtropical moisture plume has shifted well south and
east of the forecast area though a subtle H5 trough axis was still
situated through central AZ supporting some isolated light
showers/sprinkles/drizzle. In a larger synoptic sense, broad
troughing still remains the predominant feature through the SW Conus
such that little in the way of deeper subsidence and dry air
advection is occurring behind the aforementioned shortwave features
exiting AZ later today. Consequently, a shallow moist airmass will
remain in place through Wednesday afternoon creating a substantial
forecast challenge with respect to the potential for expansive low
clouds and widespread dense fog.
Confidence in HREF and global model output this evening is fair in
translating weak shortwave energy and light rainfall from central AZ
into the mountains of Gila County (and points eastward). However
given the magnitude of boundary layer moisture, any amount of ascent
could result in a few showers or sprinkles - albeit likely not
accumulating in the vast majority of locations. The larger concern
is the potential for widespread dense fog Wednesday morning. While
much of this is contingent upon breaks in the lower cloud cover
(certainly a much better likelihood across SE CA/W AZ), there are
numerous signals suggesting dense fog development even into the
Phoenix metro. First, crossover temperatures should easily be
attained tonight with no indications of horizontal advective or
vertical intrusions of drier air. Second, numerical guidance
exhibits temporal T/Td trends consistent with historical dense fog
events in the area with low temperature forecasts several degrees
below a cooling, saturated sfc profile. Within the modeling realm,
both the operational and experimental HRRR suggest wide swaths of
dense fog materializing after midnight particularly focused through
the Imperial and lower Gila River valleys. Although this model suite
has some subjective minor historical bias towards aggressive fog
formation, HREF output also supports areas of valley fog and many
BUFR sounding points display classic fog sounding profiles. Aside
from more aggressively messaging the potential for fog, have also
cut forecast highs Wednesday towards raw model output under the
assumption that low clouds and fog will be slow to burn off
effectively retarding daytime insolation.
By Wednesday night, the low amplitude western Conus synoptic trough
will shift into the plains with a high pressure ridge taking its
place through the western states. Although another Pacific wave will
break through the ridge axis late in the week effectively limiting
the magnitude of H5 heights, warming will be rather rapid across the
forecast area. With H5 heights settling into a 573-576dm range,
model spread is quite narrow showing afternoon highs fairly close to
the seasonal average Thursday, then increasing 4F-8F above normal by
the weekend. The primary uncertainty aligns with the potential for
passing high clouds and impacts on temperatures should the outcome
of cloud cover become thicker than anticipated. Ensemble and
operational models are in fair agreement that a more amplified
trough will dig towards the four corners early next week though the
more continental trajectory may limit most precipitation to higher
terrain areas of central and eastern AZ.
.AVIATION...Updated at 0052Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Light showers have mostly pushed east of the area and visibilities
have greatly improved, but SCT-BKN clouds around 1-3 kft are
expected to persist through tonight. A weak disturbance with drier
air aloft will move across the area this evening which may help
scatter out the low clouds even more. The trade-off to any
clearing overnight will be the likely development of areas of fog.
Confidence on the potential for dense fog is not high. However,
13-17Z is most likely timing for the greatest drop in visibility,
but visibility could lower as early as 10Z. By 17-18Z Wednesday,
visibility and cloud coverage should improve drastically. A light
west wind to variable is expected through most of the night,
becoming more predominantly west to southwest after 17Z.
Southeast California/Southwest Arizona including KIPL and KBLH:
A weak disturbance is passing through the area late this afternoon
bringing drier air aloft, but a few low clouds may linger through
the night. Patchy fog will be possible early Wednesday morning,
but with little to no precip falling today confidence is still too
low to mention in the TAF. Do at least show a slight visibility
drop at KIPL, to 6sm. Winds will be light and variable during the
overnight hours. becoming more northwesterly at KIPL and northerly
at KBLH after 18Z Wednesday.
Thursday through Monday:
Temperatures will warm slightly beginning Wednesday and then
remaining fairly constant by the weekend. Conditions will be mostly
dry with minimum humidity values dropping into the 20-30% range
across the lower desert and 30-40% range for the higher terrain.
Winds will remain fairly light although the Lower Colorado River
Valley may see some gusts up to 20 mph Thursday and Friday. There
are indications that another weather system could bring a slight
chance for rain early next week.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.