Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/16/18
Area Forecast Discussion
National Weather Service Denver/Boulder CO
859 PM MDT Thu Mar 15 2018
Issued at 851 PM MDT Thu Mar 15 2018
No significant changes at this time. Main center of the upper low
apparent on radar, over southeastern Weld County. As this feature
shifts to the east, then wrap around moisture will fill into the
northeast plains overnight. Best round of pcpn for the Denver area
appears to be this evening, then the focus will shift to the north
and east. Some minor adjustments in terms of timing this evening,
have delayed the higher pops by a couple of hours, otherwise will
leave the rest of the grids.
.SHORT TERM...(This evening through Friday)
Issued at 315 PM MDT Thu Mar 15 2018
Water vapor satellite imagery showing the upper level trough
tracking across the Great Basin at this time. At the surface, a
broad low is centered over east central Colorado. This surface low
is bringing northeast to east winds to most of northeast
Colorado. The easterly winds will also advect moisture into the
area. Snow showers will continue to increase over the mountains
this afternoon as the upper level trough nears the state. Showers
will progress eastward onto the near by plains late this
afternoon. Surface based CAPE climb to 200-400 J/kg late this
afternoon, so expect a few thunderstorms over the mountains and
the plains through early evening.
Going forecast of 5-10 inches of snowfall for the mountains
appear on track and will continue with the Winter Weather
Advisory. Snowfall rates under heavier showers and thunderstorms
will be near 2 inches per hour. However, this intense rate will be
Biggest forecast challenge will be the potential for snow and
strong winds on the eastern plains. The last few runs of the RAP
and HRRR have been slower with moving the surface low out of
Colorado. The latest model trends have also been a little more
north than the previous runs. The position of the surface low will
help determine where a band of rain/snow forms. Precipitation
intensity and the surface low pulling in cold air should make it
cold enough for snow after midnight across parts of the plains.
Will go with a Winter Weather Advisory for the northeast plains.
Snowfall amounts will greatly very depending on where the band of
heavy precipitation forms. A few locations may see up to 6 inches.
Winds will also be a concern as the surface low deepens. Will go
with gusts to 50 mph and blowing snow in the advisory as well. If
the low intensifies and slows even more. Some areas may need a
High Wind Warning/Blizzard Warning, all depends where the band of
As far as the High Wind Watch goes for the foothills, will cancel
it. Models do show a mean state critical layer, however winds
speeds in the models along the east slopes stay well below high
wind criteria. Will go with gusts to 60 mph at this time as it
does look windy.
.LONG TERM...(Friday night through Thursday)
Issued at 315 PM MDT Thu Mar 15 2018
After Friday`s weather system moves off to the central plains, an
upper ridge will build over the state with drier and warmer
weather. Mild southwest flow aloft will be dry. The flow pattern
across the western half of the country will be progressive as a
developing trough over the west coast moves inland Saturday night
and Sunday morning. Much like today`s upper system moving over the
desert southwest, the next trough will track eastward through
Sunday night. The latest runs of the medium range models are in
fair agreement with positioning of the upper level low over
northeast New Mexico Sunday evening. At the surface, a low
pressure area is forecast to develop over southeast Colorado. This
should produce another round of precipitation across the mountains
and northeast plains. Quasi-geostrophic diagnostics shows another
period of decent rising motion across eastern Colorado.
Temperatures will again be critical as to whether precipitation on
the plains falls as rain or snow. We will be watching the next few
runs for where the best place to put the rain/snow line on the
Monday and Tuesday look like moist westerly flow producing a
little more snow in the mountains and dry conditions on the
plains. A passing shortwave Tuesday night or Wednesday morning
will produce some more showers across the forecast area. Beyond
that, a strong ridge over the western United States will bring
drying and warming back to the region.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 851 PM MDT Thu Mar 15 2018
Areas of MVFR conditions are expected through this evening due to
showers. Still some uncertainty in the placement of precipitation
bands which could lead to lower visibilities, especially at KDEN
late this evening. Wrap around moisture from the upper trough
could impact KDEN by 06z and continue until 09z. Do not expect
cigs and vsbys to be as bad at KBJC and KAPA after 06z.
Winter Weather Advisory from midnight tonight to noon MDT Friday
Winter Weather Advisory until 9 AM MDT Friday for COZ031-033-034.
Area Forecast Discussion
National Weather Service State College PA
902 PM EDT Thu Mar 15 2018
Gusty northwest winds will continue over the local area through
Friday. Drier conditions will try to visit the region Friday
night and Saturday. A weak and fast-moving system will pass by
to our south later in the weekend, producing little or no
precipitation for the state. A larger storm system could develop
and affect the state in the middle of next week, but getting
detailed with the forecast at this point is not possible.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Another rather weak sfc and upper level trough will move
southeast from the Lower Great Lakes late tonight and help to
maintain sct-bkn high-based stratocu and altocu across the
southeast half of the CWA, while a lower bkn-ovc layer of strato
cu and occasional snow showers impacts the northern and western
mountains with light additional accumulation as vsbys briefly
dip to between 1 and 2 miles in the heavier snow showers.
Considering that the descending, thermally direct left entrance
region of a 140 kt upper jet will be drifting north toward the
region overnight, NW winds will stay gusty with sustained speeds
averaging in the mid teens, and gusts frequently in the 20 to
25 mph range.
Low temps early Friday will vary from the upper teens across
much of the northern and western mtns, to the mid 20s throughout
the Middle and Lower Susquehanna Valley. These reading will be
between 3 and 7 degrees below normal.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
Just some lingering SHSN in the morning up north, but the
sky condition should brighten later in the morning with good
downslope making it sunny in the SE. The least likely place to
see sun peek through will be those along the Route 6 corridor.
Winds will be just as gusty Fri as Thurs, maybe even more so.
So while the sun makes it feel a little nicer, the temps will
only mix up a couple kft and maxes will be in the m20s- u30s,
about 5F colder than Thurs.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
The long term will see two systems move through the region over
the next week. The first will be a closed upper level low which
will open up into a trough as it moves into the mid atlantic
Saturday afternoon. The cold air, with -5 to -10C air at 850 mb
will sit over the region well into next week. Any moisture
should remain south of the region which should allow the region
to remain primarily dry.
Moderating temperatures will allow for near normal temperatures
Sunday into Tuesday. The next system will begin to move through
the region Tuesday into Wednesday. Still quite a variability for
this system. The EC is about 6 to 12 hours slower then the GFS
with the EC having the low center further east. Latest M climate
tables keep the highest anomalies south of the region.
However there remains the possibility of a significant early
spring snowfall. The best chances will be further east, similar
to the previous Nor`easters. The high sun angle, and moderate
daytime temperatures will moderate any snowfall amounts.
.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
Cold northwest flow continues this evening. As the last few
nights, snow showers have shown a diurnal diminishment as the
evening has progressed.
However, short range HRRR shows another vorticity lobe and the
core of the coldest air rotating into the region overnight. This
is expected to reinvigorate snow showers, especially across the
Northern Mountains and Laurel Highlands.
Winds expected to stay gusty overnight. Just as with the snow,
there may be a brief period where the gusty nature of the winds
diminish, but gusts are again expected to pick up overnight with
the snow showers.
Gusty winds and improving conditions in general for Friday.
However Laurels and Northern Mountains will have a tough time
Fri...Mainly VFR, but lingering MVFR in the higher elevations of
north and west.
Sat-Mon...Mainly VFR/no sig wx.
Tues...Low cigs/vsby possible in snow/mixed precip.
Area Forecast Discussion
National Weather Service Quad Cities IA IL
648 PM CDT Thu Mar 15 2018
Issued at 343 PM CDT Thu Mar 15 2018
18Z surface data has high pressure over the upper Midwest with a
stationary front from the Ohio Valley into the central Plains. Dew
points were in the teens and 20s from the Great Lakes into the upper
Midwest and northern Plains. Dew points in the 30s and higher ran
from the lower Ohio Valley into the central Plains on south.
.SHORT TERM...(This Evening through Friday)
ISSUED AT 343 PM CDT Thu Mar 15 2018
Late this afternoon through tonight
Quiet and dry conditions will be seen from late this afternoon
through tonight. Deep dry easterly flow should prevent the
development of any precipitation in the area until after
Assessment...medium on precip occurrence/type but low on timing
The question on precipitation initiation Friday boils down to when
does the moisture overcome the dry air.
Based on RAP trends, there is a very real possibility that
precipitation initiation will not occur until late morning in the
far southwest and south areas. If this occurs, the probability
increases that precipitation will be mainly in the form of rain.
However, atmospheric profiles from the models are indicating a very
strong potential for cooling of the atmosphere when precipitation
finally initiates. This cooling may allow rain to refreeze into
sleet before it reaches the ground. If this occurs, a rain/sleet mix
would be possible on the leading edge of the precipitation before
changing over to all rain as latent heat release warms the lower
Right now precipitation should be south of an Oskaloosa, IA to
Quincy, IL by 10 AM Friday and south of a Vinton, IA to Macomb, IL
line by 1 PM. Precipitation may be as far north as an Independence,
IA to Peoria, IL line by 4 PM. There appears to be reasonable
agreement that areas north of a Manchester, IA to Kewanee, IL line
will likely remain dry until sunset Friday.
.LONG TERM...(Friday Night through Thursday)
ISSUED AT 343 PM CDT Thu Mar 15 2018
Main focus is on the system lifting out of the southwest spreading
a wintry mix of precipitation through the area Friday night into
Saturday morning. Overall forecast confidence is average to below
average due to uncertainties with the amount of moisture, timing
and thermal profiles that are critical for the precipitation
types. Sunday and beyond, the next system has trended toward a
more southerly track from previous forecasts, resulting in a much
lower impact on the forecast area with mainly rain expected. The
rest of the week looks mostly dry with near to below normal
Friday night into Saturday: Warm advection and upper level forcing
will result in widespread precipitation Friday evening. A filling
upper level low is progged by model consensus to track from
southeast Nebraska through SE IA or northeast MO overnight, while
at the surface, low pressure tracks nearly due east, just south
of this feature, spreading an inverted trough across the forecast
area. The process of top down cooling due to web bulb effects in
the initially dry low level airmass, then cold air advection as
surface winds turn northeasterly will cool the low levels
sufficiently to change the rain to freezing rain or sleet, mainly
north of interstate 80 overnight. Considering 4 inch temperatures
running in the 35 to 37 degree range this afternoon, and pavement
temperatures likely initially much warmer, the potential for
freezing rain accumulation on paved surfaces looks low. May have
ice accumulations of less than .1 on elevated surfaces overnight,
especially along the highway 30 corridor, but forecast confidence
too low this far out to go with an advisory at this time. Further
north, deeper into the cold air, where there will be less of a
warm layer aloft, the precipitation may change to snow by early
evening and remain snow until ending Saturday morning. This may
lead to up to 1 inch of accumulation of wet snow, especially
northeast of a line from Dubuque to Freeport. Far northeast MO,
southeast IA and west central IL will likely see just rain with
amounts roughly in a .10 to .25 range. All precipitation is
expected to end from west to east by mid morning Saturday,
followed by clearing skies late in the day with temperatures
returning to the 40s.
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
ISSUED AT 638 PM CDT Thu Mar 15 2018
Expect high clouds overnight with a northeast to easterly wind.
Dry air in the lower levels will help delay the onset of rain
Friday. Have timed showers into KBRL at 17z Friday, with light
rain approaching KCID/KMLI around 20z. If recent trends continue,
this timing may be delayed more.
Area Forecast Discussion
National Weather Service San Francisco Bay Area
454 PM PDT Thu Mar 15 2018
.SYNOPSIS...An active weather pattern will continue for the rest
of the week with cool temperatures and periods of rainfall along
with gusty winds at times. Dry conditions will develop over the
weekend and early next week. Wet weather will return during the
middle of next week.
.DISCUSSION...as of 01:26 PM PDT Thursday...Showers, some of them
heavy at times, blanket the Bay Area this afternoon. Overall the
last six hours rainfall amounts have varied from a few hundredths
around the South Bay/SF to a few tenths across the North Bay. Two
stations near Santa Rosa picked up just over one half inch.
Freezing levels remain relatively low 3500-4000 feet (per Santa
Rosa profiler) so wet snow or rain/snow mix seems likely over the
higher peaks. Haven`t detected any lightning strikes yet, but the
slight chance for thunderstorms remains as we approach peaking
heating of the day and a weak sfc trough off the coast approaches.
For what it`s worth the lastest HRRR still shows weak SFC CAPE
and instability through about 03Z this evening, especially the
For this evening through Friday- any afternoon convection will
diminish as surface heating diminishes. However, showers will
continue overnight and in Friday as an upper low off the coast of
OR/WA continues to move southward. Latest model guidance brings
the upper low south into far NorCal early Friday. As the low
moves south it will bring much colder air aloft. The cold core
aloft will help to lower snow levels even more than today and
introduce another chance for thunderstorms Friday afternoon. Small
hail will once again be possible Friday afternoon/evening.
Thunderstorms end Friday evening, but showers will continue Friday
night into Saturday as embedded shortwave troughs pivot around the
upper low over NorCal. Rainfall amounts Friday/Saturday will
generally be light to moderate, but given the convective nature
there will likely be some jack pots of higher amounts. Nailing
down specific snow amounts on peaks will be tricky given the
convective nature, but a few inches seems reasonable. Highest
amount currently in the forecast is six inches over the Santa
The upper low ejects to the east Saturday night into Sunday
morning resulting in a gradual drying trend. Weak ridging develops
Sunday and Monday with much warmer temperatures. One change for
early next week was to delayed the onset of the next round of
rain. Models have been trending slower with the next system and
therefore cut back on rain chances Monday night. Now for the much
anticipated possible Atmospheric River event. Not too surprising,
but the AR guidance continues to waffle along the Central Coast to
SoCal. Some guidance keeps the AR over SoCal where other guidance
aims the AR toward Big Sur. As they say, devil is in the details.
Nailing down the specifics of an AR this far out it is hard, but
it is easier to say the middle of next week continues to look
rather wet. Latest forecast will have wet weather for the entire
Bay Area Tuesday through Thursday. Given the subtropical tap
rainfall amounts will likely be higher than the showery regime
we`ve been in lately.
.AVIATION...as of 4:52 PM Thursday...For 00z Fri Tafs. KMUX radar
shows scattered showers moving through the area, moving in a WSW
to ENE motion. Current cigs are generally above 3000 feet across
the region, with a few MVFR cigs in the SF Bay Area and North Bay.
Cigs will likely lower over the next few hours, and MVFR cigs are
expected to dominate this evening. Scattered showers are forecast
to continue through much, if not all, of the TAF period. Thus,
kept -shra in the TAFs for all terminals. The most tricky part of
the forecast will be cig heights. Generally, expect intermittent
VFR/MVFR cigs through tomorrow, with possible IFR conditions in
heavier showers. A cold front will pass through the area sometime
between midnight tonight and sunrise tomorrow morning. Winds will
turn west-southwest and become gusty along and behind the front.
Gusts over 20 knots are possible behind the front.
Overall forecast confidence: Low to moderate
Vicinity of KSFO...Generally MVFR through tonight, with
intermittent showers. Southwest winds will remain breezy tonight,
sustained around 12-15 kt, and may decrease some after midnight.
Winds will then increase again and become gusty behind a cold
front tomorrow morning, gusting over 20 knots through tomorrow
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Currently, cigs are above 3000 feet at
KMRY and KSNS. Anticipate cigs to lower through the evening, with
showers continuing through the night. Breezy
southerly/southwesterly winds this evening, 10-15 knots, with
occasional gusts above 20 knots. Winds will increase and become
gusty behind a cold front that is forecast to pass through
tomorrow morning. Exact timing of the FROPA is still unknown at
.MARINE...as of 08:24 AM PDT Thursday...Winds will remain light
to moderate today as a cold front is expected to move through the
coastal waters this afternoon and tonight. Along with this front
will come scattered showers and a slight chance of thunderstorms
in the afternoon. Active weather is expected to continue through
the forecast period.
PUBLIC FORECAST: MM
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