Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/17/18
Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
947 PM CST Sun Dec 16 2018
The forecast is in good shape with just a minor addition to the
weather grids needed tonight.
The plume of dense mid and upper level clouds continues to
infiltrate the region ahead of an upper trough situated across
Sonora and Chihuahua. Short term guidance has a good handle on
this and it`s likely that most of the area will stay socked in
beneath cloud cover through the overnight hours into Monday
keeping temperatures a few degrees warmer than the previous night.
Cloud cover may think some along the immediate Red River Valley
and this has implications for the fog forecast tonight. A very
diffuse boundary continues to slide southward through North Texas
at this hour. Outside of a subtle wind shift to the
north/northwest, the only real impact from this boundary will be
to help generate a reservoir of low level moisture that could lead
to some fog development. The most likely area where fog will
develop will be across the Ark-La-Tex where surface dewpoints are
a little higher with values in the upper 30s and low 40s. Forecast
profiles from the 3km NAM and RAP near Paris do support a good
chance for radiation fog and experimental visibility products
indicate that some of the fog may become dense. I`ve only added a
small sliver of patchy dense fog wording to parts of Fannin,
Lamar, Delta and Hopkins counties given that the lingering cloud
deck---though thinning---may keep T/Td spreads up a little higher
than I`d like to see for widespread dense fog. Nevertheless,
there still remains a chance that visibility reductions of 1/4
mile may occur...mainly in low-lying and sheltered areas...as
well as near bodies of water.
The rest of the forecast is in fantastic shape and updated
products have been sent.
.AVIATION... /Issued 605 PM CST Sun Dec 16 2018/
00 UTC TAF Cycle
Concerns---None major. Low MVFR vsby potential at DAL and GKY.
Dense mid and upper level cloud cover will continue to obscure the
Texas sky through the 00 UTC TAF cycle with cigs between FL150
and FL200. Across North Texas, light southerly breezes will become
westerly with a weak FROPA around 0300 UTC and this may
necessitate a flow change at D10 airports. Winds will turn more
northerly just after midnight with northerly breezes expected
through Monday evening. Across Central Texas, winds will be a
little slower to turn westerly and northerly with the windshift
likely closer to midnight. A sufficient reservoir of moisture is
expected to develop ahead of the front and may result in some
reductions in visibility. All indications at this juncture,
however, indicate that the probability of this occurring in the
Metroplex is NOT very high and I`ve refrained from including BR in
the TAFs. IF BR does occur at Metroplex TAF sites... DAL and GKY
would stand the best chances to see reductions in vsby given
their closer proximity to the near-surface moisture reservoir.
.SHORT TERM... /Issued 252 PM CST Sun Dec 16 2018/
Widespread high clouds have streamed over the area today ahead of
a deepening southern stream upper low. Despite nearly overcast
skies through much of the day, temperatures have still managed to
climb into the mid 60s in most areas thanks to the return of
Meanwhile, a slow-moving cold front lies to our north through the
Texas Panhandle and southern Oklahoma. Later this evening, a
shortwave swinging southward through the Central Plains will send
this very weak cold front into North Texas. This feature is
essentially just a surface trough, as there is little in the way
of cooler or drier air behind it. The only noticeable effect it
will have on sensible weather will be to turn winds to the west
and eventually to the northwest late tonight, but wind speeds will
remain fairly light. One side effect of this front will be the
potential for patchy fog to develop across portions of northeast
Texas Monday morning, likely just northeast of the DFW Metroplex.
Nearly calm winds and some pooled moisture should contribute to
at least some patchy fog development, although widespread fog may
be hindered by the presence of mid/high clouds which would inhibit
optimal radiation fog conditions. have included patchy fog in the
forecast for the time being, but localized dense fog is certainly
a possibility that will need to be monitored overnight.
.LONG TERM... /Issued 252 PM CST Sun Dec 16 2018/
/Monday through Next Weekend/
The disturbance currently over northern Mexico will lift northeast
across Texas on Monday, generating little more than increasing mid
and high level clouds along with the possibility of a few
sprinkles. It will also be accompanied by a weak cold front,
which will bring light northwest winds and knock a degree of two
off tomorrow`s high temperatures.
Return flow will quickly resume Monday night and Tuesday as a more
robust shortwave crosses the Four Corners region on its way east
towards the Plains. Between the two systems, light southeast winds
and mostly clear skies may allow for fog development during the
Monday night / Tuesday morning period. Patchy fog has hence been
added for the central and southeastern counties where the lesser
dewpoint depressions will be.
Scattered showers should begin to develop Tuesday late afternoon
or evening as the shortwave trough axis approaches from the west
and forcing for ascent increases over North and Central Texas.
The "evening" seems more likely due to the atmosphere being
initially starved of moisture as lift first arrives. PWATs will
eventually climb into the 0.85-1.0 inch range overnight Tuesday
night into Wednesday with the higher values east of the I-35
corridor. POPs will likewise be oriented with the highest in the
east. Instability will be limited, with surface-based CAPE values
of only a hundred or so forecast at this time, but mid level lapse
rates will be steep enough to warrant the mention of isolated
Precipitation will end across the western counties early
Wednesday, then move east of the entire forecast area by
Wednesday evening as the shortwave continues east.
The upper air pattern will amplify Wednesday night and Thursday
as another disturbance drops southeast through the Plains and
merges with the initial shortwave. The result will be a rapidly
deepening upper low over the Mississippi Valley on Thursday. This
will draw cool continental air farther south, and have sided with
the cooler end of guidance for the extended forecast temperatures.
At this time, it looks like all precipitation associated with the
upper low will remain east of the forecast area, and a dry
forecast will remain in place for late week into next weekend.
.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 42 59 42 65 50 / 0 0 0 5 50
Waco 43 62 39 65 49 / 0 0 0 5 40
Paris 40 58 42 61 47 / 0 0 0 0 50
Denton 38 57 39 65 48 / 0 0 0 5 40
McKinney 38 58 40 62 50 / 0 0 0 5 50
Dallas 43 59 43 65 50 / 0 0 0 0 50
Terrell 41 58 41 64 50 / 0 0 0 0 50
Corsicana 44 60 43 62 51 / 0 0 0 0 50
Temple 43 63 41 65 48 / 0 0 0 5 40
Mineral Wells 38 58 39 64 46 / 0 0 0 10 40
Area Forecast Discussion
National Weather Service Green Bay WI
537 PM CST Sun Dec 16 2018
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Monday
Issued at 217 PM CST Sun Dec 16 2018
The latest RAP analysis and satellite/radar imagery show a surface
trough or weak cold front moving across eastern WI early this
afternoon. Colder air is lagging behind the front and over
northwest WI. Only mid and high clouds are present along the
front, while an area of low stratus is pushing into northern Lake
Superior deeper into the colder airmass. With relatively quiet
conditions expected, cloud trends and temps continue to be the
main forecast concerns.
Tonight...Winds will gradually veer around to the northwest and
draw in some that colder air over northern MN as high pressure
moves towards the region. Low level temps are projected to be
marginally sufficient for lake effect snow showers over western
Lake Superior, and the hi-res models continue to show some light
returns are possible. Will therefore keep a chance of flurries
over the northern WI snow belt after midnight. The rest of the
area should see mostly clear to partly cloudy skies with a breezy
west to northwest wind. The wind should hold temps up, so didnt
change temps much from the previous forecast.
Monday...High pressure will settle across the area in the
afternoon. Northwest winds will continue to bring a chance of
flurries to the northern WI snow belt in the morning, before drier
air with the incoming high causes any snow showers to retreat to
the north. Mostly sunny conditions are expected elsewhere. Temps
will fall back closer to seasonal norms, with highs ranging from
the upper 20s in the north to mid 30s near Lake Michigan.
.LONG TERM...Monday Night Through Sunday
Issued at 217 PM CST Sun Dec 16 2018
A high pressure ridge will promote warmer conditions through
Tuesday with no rain or snow expected. Precipitation chances
arrive on Wednesday as low pressure troughing develops in the
nation`s mid-section and pulls Gulf of Mexico moisture north to
the Great Lakes. A cold front will sweep through Wisconsin on
Thursday, but moisture aloft will continue to flow into the region
through Thursday night. A mixed bag of precipitation is likely as
the cold air mass from the northwest and the warm air mass from
the southeast duke it out for control over Northeast Wisconsin.
Colder temperatures and drier conditions are expected for Friday
and Saturday in the wake of the cold front, with only a slight
chance for precipitation through Sunday.
.AVIATION...for 00Z TAF Issuance
Issued at 537 PM CST Sun Dec 16 2018
VFR conditions expected through Monday everywhere except
north of a Rhinelander to Iron Mountain line where there will be a
period of MVFR ceilings and snow flurries late tonight through about
Low level wind shear is possible through the mid evening hours tonight
with northwest winds around 35 knots at 2000 ft and west winds around
10 knots at the surface.
Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
912 PM CST Sun Dec 16 2018
Updated for evening discussion.
Most of the clouds have cleared for the night leaving room for
some radiational cooling. The surface high has positioned its self
over our area and with this cooling, there will be widespread fog
tonight with greatest potential to become more dense after 6z
continuing in to early Monday morning according to the HRRR, and
with confidence this shall prevail. We have issued a dense fog
warning across the entire CWA starting at 12am. Lows will be in
the lower 40s all across our area. /JE/
Prior discussion below:
Tonight and Monday: While the majority of the stratus deck has
cleared the area, somewhat thick cirrus shield has overspread aloft
in advance of developing mid level storm system to the west. Cirrus
has been pretty much unimpeded as it has spread east today, but that
looks to change a bit moving into the evening. As the storm system
digs over northwest Mexico this evening, ridging will develop to its
east. This will serve to diminish the high level cloudiness tonight
as subsidence increases on the eastern side of the ridge.
The thinning cirrus tonight will allow for good radiative heat loss
and decoupling as the surface high center becomes positioned over
the forecast area. With nothing to scour out the residual boundary
layer moisture, cooling tonight should allow for widespread fog
development, becoming somewhat dense toward sunrise Monday. With the
HRRR and NAM giving strong indications of widespread dense fog will
issue a dense fog advisory for the entire area to begin after
Monday night through Tuesday: Looks generally quiet until
Wednesday when the next system comes through the area.The models
are in good agreement that an upper low will develop in the long
wave pattern as a deepening surface low tracks across the Arklatex
into NW MS. GFS does not show much instability and lapse rates
were not great. However the low level jet looks good and there was
some 40kts or more of shear late Wednesday afternoon into the
evening. Kept chance of thunder wording in the forecast for the
entire area Thursday afternoon/evening. Looks like rain will move
in early, so storm development should be elevated. As the surface
feature moves north, we get a period of dry air before the
shortwave and wrap around moisture eventually move east. Thursday
looks to be overcast with light rain likely. Models actually show
the system slowly moving out of the area, so went with it. High
pressure move in for the weekend. Models suggest a weak trough
will pass through the area, bringing clouds. Not looking for much
rain so kept the area dry through the weekend. The next storm
system moves around Tuesday of next week with a low pressure and
cold front expected to move through the region.
Temperatures seem ok. Should be cold behind the boundary this
week,especially with clear skies likely Thursday night/Friday
night. Clouds may keep things above freezing Saturday night/Sunday
Night, so raised values a degree or two. Overall, big changes to
the forecast. /7/
00Z TAF discussion:
VFR conds were reported areawide at 2330Z and VFR conds wl pevail
this evening but after 06Z fog development is expected. Areawide
LIFR conds are expected by 11Z and wl cont until 15Z. VFR conds
are expected to prevail areawide after 15Z Monday. /22/
.PRELIMINARY POINT TEMPS/POPS...
Jackson 41 63 40 62 / 0 0 3 3
Meridian 41 64 39 62 / 0 0 3 2
Vicksburg 42 63 41 63 / 0 0 2 3
Hattiesburg 41 64 41 63 / 0 0 1 1
Natchez 41 65 42 64 / 0 0 2 2
Greenville 42 59 41 59 / 0 0 4 3
Greenwood 42 60 40 60 / 0 0 4 3
MS...Dense Fog Advisory from midnight tonight to 10 AM CST Monday for
LA...Dense Fog Advisory from midnight tonight to 10 AM CST Monday for
AR...Dense Fog Advisory from midnight tonight to 10 AM CST Monday for
Area Forecast Discussion
National Weather Service Mount Holly NJ
935 PM EST Sun Dec 16 2018
Low pressure will continue to move away from our area tonight as
high pressure begins building in from the west. High pressure will
persist through the middle of the week before moving offshore,
then an expansive and strong area of low pressure moves into the
region by the end of the week.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
The Winter Weather Advisory was allowed to expire at 9 PM. The
main wintry precipitation has ended, although some flurries or
a brief snow shower cannot be ruled out the rest of this
evening in the Poconos. Otherwise, the closed low continues to
shift away from our coast taking the surface low with it.
Residual lift on the backside of these features continues to
rotate some rain showers into portions of coastal New Jersey.
These are expected to shift offshore by Midnight. Some mist or a
brief light rain shower may persist into the Philadelphia metro
area for a few more hours before enough drying gets pulled farther
eastward. Plenty of clouds remain across the region, and these
may tend to stick around for much of the night.
For the 930 PM update, made some tweaks to the hourly temperature,
dew point and wind grids based on the latest observations and
trends. Adjusted the PoPs to show a faster decrease from west
to east given ongoing radar and HRRR trends. The persistent
cloud cover should limit radiational cooling.
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
The evening updates increased the wind and wind gusts especially
for the afternoon. Tightened pressure gradient combined with
deeper mixing will result in a gusty wind. The forecast soundings
show about 30 knots of wind available to mix down. These soundings
also show the potential for a decent amount of stratocumulus
occurring, and therefore increased the cloud cover south and eastward
through the afternoon. The increased cloud cover however could
lessen the deeper mixing, but overall a breezy day is expected.
Otherwise, strong northwest flow is expected on the backside of
the departing low. In addition, a mid level short wave trough
is expected to quickly dig SE along the northern portions of the
region. The combination of these factors could lead to some
snow showers reaching the southern Poconos and Northwest NJ,
though the bulk of the activity will be north and west of our
region. Temperatures are expected to be near normal, with highs
ranging from the mid 30s to lower 50s.
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
By late Tuesday, the building high pressure will continue to clear
things out across much of our area. Gusty winds from late Monday
will persist through the overnight hours and into early Tuesday
before relaxing Tuesday night as the high shifts just south of our
area. Winds could potentially gust over 30 mph early Tuesday
evening. Temps will fall into the mid to upper 20s Monday night with
radiational cooling being greatly suppressed due to a coupled
boundary layer and subsequent steady breeze overnight. Expecting
Tuesday to be an exceptionally clear, but chilly day with highs only
topping out in the upper 30s to low 40s. As winds diminish Tuesday
evening, temps will quickly fall into the 20s. Clear and cold will
remain the story Tuesday night with temps bottoming out in the low
to mid 20s by Wednesday morning. Fair weather is expected to
continue into Wednesday as high pressure pushes offshore with clouds
moving back into the region by later in the day and highs topping
out in the low to mid 40s. Not as cold Wednesday night with
increasing cloud cover and lows around normal for this time of year.
By early Thursday, a high amplitude upper trough will be digging
south across the southeastern US and Gulf of Mexico. A large, strong
area of low pressure is expected to develop across the southeastern
US on Thursday bringing the potential for some light rain showers
during the day with chances increasing into the late afternoon and
evening hours. This system appears to be warm enough to bring only
rain to our entire area at its onset.
This next storm system begins to move into the area Thursday
night into the day Friday. Not a whole lot of change in the
timing or placement of the system. Guidance seems to be
continuing agreement on the low moving up the Appalachians/Ohio
River Valley to our west during the Friday/Saturday timeframe.
The GFS and ECMWF continue to forecast the development of a
well-defined synoptic trough over the eastern U.S. by Thursday.
Several factors including broad mid to upper-level diffluent
flow, appreciable positive vorticity advection, and a jet streak
located over the Northeast/Canadian Maritimes all support the
development of a strong extratropical cyclone. As noted in
previous discussions, this places us in the warm sector under
the influence of what appears to be fairly substantial warm air
advection ahead of the system. Bumped up highs Friday from
yesterdays forecast a few degrees-now ranging from the low 50s
across the Poconos to near 60 across southern Delaware. Friday
will likely have the feel of a Spring day rather than that of
mid-December; take it or leave it as you see fit. Cooler as the
surface low begins to pull to the northeast out of our area
Saturday, returning us to northwest flow.
After a brief lull, additional precip is expected to wrap around the
surface low Saturday and early Sunday. As cold air advects into the
region, some of this could fall in the form of snow showers through
the northern half of the forecast area including the Lehigh Valley,
Poconos, and NW New Jersey. Highs Sunday will range form the low 30s
north to upper 40s south. Dry weather should return to most, if not
all the area Sunday night.
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Tonight...Rain is coming to an end across the area, however, MVFR or
IFR ceilings will remain for much of the evening and overnight
hours. An improvement will occur for all sites through the overnight,
with some improving to VFR earlier, and others not until late in
Winds remain mostly out of the north to northwest around 10 knots,
with ACY and MIV even stronger winds and gusty around 20-25 knots
for a few more hours. Winds will shift more toward the northwest
overnight around 5-10 knots everywhere.
Monday...Conditions expected to start the day off VFR, with
increasing clouds through the afternoon. ABE and RDG may have their
ceilings lower to MVFR, while the rest of the area is expected to
Northwesterly winds are expected to increase to 12-18 knots with
gusts to 25-30 knots, with the strongest winds during the afternoon.
Monday night...mostly VFR conditions are expected. West to
northwesterly winds through may gust up to 25 kt through the
evening hours. A steady breeze is expected to last through the
Tuesday through Tuesday night...VFR conditions expected. A steady
breeze is expected with northwesterly winds gusting up to 25 kt
during the day.
Wednesday and Wednesday night...VFR conditions expected with light
west to southwesterly winds.
Thursday through Friday...VFR expected early Thursday with scattered
rain showers increasing in coverage through the day. MVFR or IFR
possible Friday morning as heavier showers move across the area.
Southerly winds may gust up to 20 knots Friday.
Small Craft Advisory through tonight for all of the Atlantic
coastal waters as low pressure gradually moves away. The Small
Craft Advisory for Delaware Bay goes through Monday night,
despite probably a lull in the winds for a time later tonight
before ramping back up again during Monday. It is possible this
may need to be upgraded to a Gale Warning at least for the lower
portion of the bay. Held onto the Gale Watch for now for the
Atlantic coastal waters which starts Monday afternoon. Increased
the wave heights on the ocean based on current observations,
then slowed the decrease some through the evening.
Monday night...SCA conditions expected to continue with Gale
force gusts possible.
Tuesday through Tuesday night...SCA conditions expected to last
through Tuesday evening with Gale force gusts possible in the
morning, otherwise sub-SCA conditions expected overnight Tuesday
Wednesday through Wednesday night...Sub-SCA expected.
Thursday through Friday...SCA conditions possible by late Thursday
night with southerly winds gusting near 25 knots and waves
increasing to 5-8 feet into Friday.
MARINE...Gale Watch from Monday afternoon through Tuesday morning for
Small Craft Advisory until 6 AM EST Monday for ANZ450>455.
Small Craft Advisory until 6 AM EST Tuesday for ANZ430-431.
Area Forecast Discussion
National Weather Service Pocatello ID
847 PM MST Sun Dec 16 2018
.UPDATE...Late evening update to slow down the entrance of PoPs
tonight, outside of the central mountains. As of about 9pm, radar
echoes continue to inch towards our western flank, but little
appears to be reaching the ground, save for across the Sawtooths.
00z models continue the slowing trend seen in their hi-res
brethren. With this in mind, delayed the onset of precipitation
across the eastern Magic Valley. Otherwise, the rest of the
forecast seems on track.
.PREV DISCUSSION... /issued 206 PM MST Sun Dec 16 2018/
SHORT TERM...Tonight through Wednesday morning. Early afternoon
satellite imagery was showing an elongated upper trough advancing
toward the west coast as attending precipitation lifted north
through NRN California, Oregon, and Washington. The GFS and NAM were
in good agreement through the period with moderate to heavy
precipitation spreading north through the WRN states today and this
evening and into WRN Idaho overnight but then rapidly dissipating as
the trough continues to advance east into the Great Basin Monday
afternoon/evening resulting in light snow accumulations across most
of SE Idaho and upwards of 4 inches in the CNTRL Idaho mountains
from Ketchum north through Stanley. Once again this mornings model
runs were showing a warm layer aloft over sub-freezing temperatures
in the Burley area Monday morning but with much drier low level
conditions which will most likely limit the potential for freezing
rain. We fall between systems Monday night as the next system takes
shape off the NW coast. The leading edge of this second system
begins to spread into the CNTRL mountains Tuesday morning with
increasing precipitation potential across the NRN mountains Tuesday
and all of SE Idaho Tuesday night as the disturbance shears east
through the region. We will likely see strong gusty winds Tuesday
afternoon and night as a 150kt upper level jet streak traverses the
region. The combination of wind and moderate snow accumulations of 4
to 10 inches Tuesday through Tuesday night from Ketchum to Stanley
in the CNTRL mountains and from Palisades northward through Henrys
Lake along the Wyoming border should be enough to satisfy a Winter
Weather Advisory for those regions. I would fully expect to see
those highlights issued with the Monday afternoon package. Huston
LONG TERM...Wednesday through next Sunday Night. This period is
marked by a flat 500mb longwave pattern initially, amplifying to a
Pacific coast ridge and eastern Great Plains trough by Fri, then
shifting very slowly eastward and de-amplifying by Sun, with the
upper level ridge inland and the trough over the Great Lakes region.
This scenario puts the storm track initially over Idaho, but then
pushes it farther north towards the end of the period, allowing some
drying, and with higher 500mb heights, possibly some warming.
However, the de-amplifying makes it easier for shortwaves to break
down this weakened ridge and move into the Gem State. Factoring in
shortwaves, the ECMWF and GFS are in good agreement with the strong
storm on Tue night winding down during the day Wed, a quiet Wed
night and Thu with a weak upper level ridge, then that ridge
breaking down Thu night and spreading rain/snow into the forecast
area with moderate precipitation amounts in the central Idaho
mountains and the ID-WY border region from Blackfoot Reservoir north
to the two National Parks. Up to this point, the GFS and ECMWF have
some pretty amazing agreement on precipitation amounts and
geographical placement. After a quiet Fri night, the guidance
product solutions start to differ, with the GFS bringing in a very
weak wave to keep some light precipitation going, while the ECMWF
has a strong upper level ridge develop. Finally the last 24 hours
(Sun/Sun night) the two models bring some moderate to heavy
precipitation into central and eastern Idaho. The GFS is wetter and
has it coming from the west northwest, looking very much like an
atmospheric river event. The ECMWF is more of an individual
shortwave coming from the southwest and swinging through the
forecast area. Messick
AVIATION...Gradually thickening and lowering clouds are expected
over the next 24 hours for KPIH and KIDA, but both terminals should
ride solidly VFR through at least 18Z Monday. The same is expected
for KDIJ, but here we added LLWS overnight tonight into Monday
morning as southwest winds increase aloft over a decent surface
temperature inversion. NAM BUFKIT soundings indicate this shear more
strongly than most of the rest of the guidance, but think surface
winds will decouple from the overall flow a bit more effectively in
this inversion regime than some of the models suggest, and the
period of concern is over a pretty long duration. Slight chance for
a more brief period of LLWS at KBYI late tomorrow morning, but with
less confidence and a shorter 3-4 hour window of concern (about 16Z
to 20Z), left it out of the TAF for now and will let evening shift
reevaluate for the 00Z or 06Z TAFs. Despite fairly strong inversions
and potentially slightly lighter winds than last night, the
combination of gradually increasing clouds, a lack of recent
precipitation, and SLIGHTLY larger temperature-dew point depressions
on MOS guidance would suggest fog and low stratus should not be a
concern tonight for KPIH/KIDA/KDIJ. The HRRR surface visibility
product also isn`t lighting anything up. (Basically, if it didn`t
happen last night, it likely won`t happen tonight.) Meanwhile, VFR
conditions with increasing clouds are expected for KBYI and KSUN as
well, but precipitation is likely prior to the end of the TAF period
ahead of our next approaching storm system. Timed this out in the
TAFs using the high-res HREF ensembles and NAM time-height plots,
which all showed reasonable agreement. VFR to MVFR conditions are
likely at KBYI near and just after the end of the 18Z TAF period,
with slightly warmer temperatures and and attendant possible
changeover to rain reducing some of the risk of low vsbys. Greater
impacts are expected at KSUN, however, with MVFR to IFR conditions
likely from about 11Z onward through the rest of the day/evening.
Undercut model guidance a bit here for cigs/vsbys based on copious
low-level moisture and MOS numbers, but held the terminal above
airfield minimums. - KSmith/Messick
Area Forecast Discussion
National Weather Service Tucson AZ
845 PM MST Sun Dec 16 2018
.SYNOPSIS...Isolated showers producing light rain mainly east of
Tucson ending late tonight. A passing system will bring isolated to
scattered rain and snow showers mainly across the White Mountains
Monday afternoon and Monday night. Otherwise, dry conditions into
next weekend. Seasonably mild daytime temperatures Monday and
Tuesday followed by a strong warming trend later in the week.
.DISCUSSION...Isolated showers producing sprinkles to light rain
were occurring across eastern Pima County including the Tucson metro
area, western Cochise County and across Santa Cruz county at this
time. Rainfall amounts that have been recorded since this afternoon
have been mainly confined to southwest Cochise County and Santa Cruz
County, with amounts generally under one tenth of an inch. However,
a few higher amounts were around 0.25" to 0.35".
Otherwise, IR satellite imagery and surface observations depicted
cloudy skies across much of this forecast area at this time. The
exception was across western Pima County where mostly clear skies
were noted. Colder-topped clouds were from Tucson northward and
northeastward into southeast Pinal/western Graham Counties. Dew
points at lower elevations valid 8 pm MST ranged from the lower 20s
near Safford to the 30s-lower 40s elsewhere. A dew point jump at
KTUS from the lower 20s to around 40 degrees occurred from 6:30 pm -
8 pm MST.
Several HRRR solutions were quite similar with moving the ongoing
band of light rainfall across eastern Pima County northwestward
into southern Pinal County and dissipating by around 11 pm MST.
However, other isolated showers should occur east of Tucson later
tonight as the upper trough responsible for this precipitation moves
eastward into New Mexico. Dry conditions should prevail across much
of the area Monday morning, then isolated to scattered rain/snow
showers mainly across the White Mountains Monday afternoon and
Monday night associated with another upper trough moving across the
Four Corners region.
Otherwise, dry conditions into next weekend. Seasonably mild daytime
temperatures Monday and Tuesday followed by a strong warming trend
later in the week as high pressure builds over the area. The
official forecast was updated as a few minor adjustments were
made to precip chances and sky condition the rest of tonight and
Monday morning. Please refer to the additional sections for further
.AVIATION...Valid through 18/06Z.
Isolated -SHRA mainly east of KTUS ending by daybreak Tuesday.
Isolated to scattered -SHRA/-SHSN mainly across the White Mtns
northeast of KSAD Monday afternoon and evening. Otherwise, east
and south of KTUS expect SCT-BKN clouds at 4k-8k ft AGL becoming
SCT-BKN clouds mainly above 8k ft AGL Monday afternoon. KTUS
vicinity northwestward expect SCT-BKN clouds 6k-10k ft AGL becoming
SCT-BKN clouds mainly above 12k ft AGL Monday afternoon. Surface
wind variable in direction under 12 kts through valid period.
Aviation discussion not updated for TAF amendments.
.FIRE WEATHER...Isolated to scattered rain and snow showers mainly
across the White Mountains Monday afternoon and Monday night.
Otherwise, dry conditions into next weekend. Mild daytime
temperatures through Tuesday before a strong warming trend later in
the week. 20-foot winds will be terrain driven under 15 mph into
.PREV DISCUSSION /205 PM MST/...Convective allowing models depict
light shower activity this afternoon through this evening primarily
over sections of Santa Cruz and Cochise Counties. The 12Z GEFS
plumes produce measurable rainfall among all ensemble members at
KDUG, albeit meager amounts averaging a tenth of an inch. Showers
generally ending later overnight, shifting the focus more toward the
White Mountains as a second upper trough grazes the northeast corner
of our forecast area. The best chance for precipitation occurs
Monday evening, and snow levels will drop overnight to around 6000-
7000 feet. Conditions then dry out Tuesday morning as the trough
An anomalous 500mb high then begins to build in on Wednesday,
producing a steady increase in temperatures. NAEFS mean 500mb
heights are above the 90th percentile beginning Wednesday through
part of Friday. Anticipate some of the warmest high temperatures
measured since late November on Thursday/Friday. A weak upper trough
passes over the weekend, nudging temperatures back down and
temporarily increasing cloud cover. No precipitation is expected.
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