Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/13/17
Area Forecast Discussion
National Weather Service State College PA
1026 PM EST Thu Jan 12 2017
A cold front is exiting the southern tier of PA. High pressure
will build into the region on Friday. An anomalous upper level
ridge will build over the southeast United States this weekend
into early next week. At the surface, a quasi-stationary frontal
boundary will oscillate in the vicinity of PA through early next
week. Milder conditions will work back into the area for mid week.
.NEAR TERM /UNTIL 9 AM FRIDAY MORNING/...
The wind has picked up across the central mountains, and expect
just a little more wind through the night in the ern valleys.
Rivers behaving as expected right now with Wilcox gage turning
around. So, Johnsonburg should be OK staying just below FS. Temp
close to freezing in the NW, so any wet ground/pavement may become
Wind has switched to the NW at most sites. However, the light wind
in the eastern valleys is allowing fog to form. As of yet, no
M1/4SM obs. But, if the wind does not pick up a few knots, it may
get dense. Rain band breaking up and getting lighter. Rain has
ended in the NW, but some flooding is still on-going. Latest
reports indicate few if any new areas of flooding have developed
in the last couple of hours. Have therefore canceled the flood
watch. What is on-going should start to recede soon - but the
larger waterways, esp the Conewango Creek in Russell, will rise a
Front is through 85% of the area at 7pm/00z. Precip is holding
together slightly better than expected, but is on the wane. Wind
is still light in the ern valleys and some fog has started to
form. while winds will not be all that strong overnight, the fog
should not get dense as there will be some gradient wind. Temps
will be getting cool enough by midnight in the NW that if
something were to fall, it could be flurries or sprinkles or some
fzdz. Will have to watch for that possibility.
Radar continues to show moderate to heavy rain moving across my
NWRN counties. Flood advisories continue for reported minor
flooding as snow melt, rainfall and frozen ground conspire to
cause rapid runoff.
The latest HRRR shows the heaviest rain beginning to move
southeast out of the northern mountains by mid afternoon so
conditions should begin to improve over the next 3-6 hours.
Will maintain POPs at or around 100% across the northwest
counties, while the southern half of the state should see no more
than a passing shower at times through 3PM. With the showers
expected to diminish as they enter the central counties and lower
Susq, I tapered the POPS to cover this. Guidance further suggests
the rain that makes it into my southern counties will taper off
rapidly between about 6 and 9 pm tonight, leading to a mainly dry
overnight. As of right now I expect enough post frontal
cloudiness to keep fog from becoming a widespread problem. But if
we scatter out, that will change.
Another threat will be for an isolated severe storm. Meso anal
shows a nose of meager Cape but with intense windshear nosing
into western Pa along and just ahead of the surface front.
Lightning data shows an occasional cluster of strikes indicating
thunder is occurring. SPC has a marginal risk up into western Pa
so the potential for a strong wind gust cannot be ruled out with
any potentially well organized convection.
Lows will range from the mid 20s over the NW to around 40 over the
.SHORT TERM /9 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
Friday looks basically dry with brightening skies as cooler and
drier air works in from the north and west. Highs will be 20 to
30 deg cooler than today.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Did not change much for the weekend.
Colder air at low levels this weekend will keep the risk of mixed
precipitation across the area on Saturday, and again by the later
part of Monday. Main area of concern will be the southern part of
central PA. Not looking at much QPF with either system, but type
of precipitation being the concern.
More detail below.
This weekend, central PA will be in between an anomalous upper
ridge over the southeast conus and shortwave traversing southeast
Canada. At the sfc, a weak wave of low pressure is progged to pass
south of PA along a quasi-stationary front. A period of light
snow or wintry mix will likely accompany this feature Sat/Sat
evening, mainly across the southern counties. Fairly good
agreement among med range guidance for a dry/seasonable Sunday, as
high pressure builds southeast into the region. Main change was to
edge a little precipitation a few miles further north.
Next week looking mild and showery, as bulk of med range guidance
shows a building ridge along the east coast with a surface low
track west of PA. It looks like there will be enough low lvl cold
air to support some ice ahead of first low on Monday.
For Tue-Thu, med range guidance placing PA in deep southerly flow
ahead of a trough over the midwest. Plume of anomalous PWATS over
the region supports the idea of warm and showery weather. GEFS
temp plumes showing no below freezing temps (even at BFD) Tuesday-
Some variation with potential waves on the front by late next
week, thus did not want to take mention of showers out for late
Thursday at this point.
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
A cold front will exit the southern tier of PA this evening. High
pressure will build into the region on Friday.
Rain band in association with the cold front was earlier much more
notable with a period of heavier rain and gusty winds, but at 02z
it is quickly diminishing as it pushes across the southern
mountains and Lower Susquehanna Valley. LLWS also coming to an end
as parent low tracks further into New England and low level flow
weakens a bit as it turns to the west.
Winds at the surface will pickup as the night wears on - they
already have across portions of the west. But until they do, the
light winds and plentiful ground moisture will bring areas of
fog - some dense - to the valleys of the east (including KIPT).
This should mix out overnight as winds increase with drier air
moving in. Over the west, upslope flow should keep IFR/MVFR in
place through much of the overnight before gradual improvement Fri
morning - as KBFD looks to be the last to improve to VFR.
Developing downslope flow will bring improvement to VFR early
overnight to the central mtns.
Fri...Mainly VFR with decreasing winds.
Sat...Sub-VFR likely with wintry mix southern 1/2 airspace.
Mon-Tue...Sub-VFR likely with another period of mixed pcpn psbl.
Daily max temperature records for today...
Harrisburg 60/1890 == 65 today
Williamsport 57/1986 (55 today)
Altoona57/2006 == 66 today
Bradford 53/2013 == 56 today
Johnstown 66/1898 (63 today)
NEAR TERM...Dangelo/La Corte
SHORT TERM...La Corte
Area Forecast Discussion
National Weather Service Lubbock TX
907 PM CST Thu Jan 12 2017
Issued a Freezing Rain Advisory for locations mainly along and
east of I-27 and north of US 70 beginning overnight and continuing
through the day Friday.
Latest observations from the West Texas Mesonet indicates
localized area of 32F-33F surface temperatures on the Caprock from
Silverton and Tulia south to Plainview and Floydada. This pocket
of cooler air has been handled reasonably well by mesoscale models
this evening with the past two runs of the HRRR showing
increasing amounts of accumulating freezing rain over this same
area through noon tomorrow, likely a result of enhanced upslope
flow. Surface wet-bulb temperatures drop into the mid 20s and
remain there through much of the afternoon tomorrow as
drier/colder air continues to hold in place on northeasterly
winds. Above the shallow cold dome, increasingly moist but shallow
isentropic lift occurs creating a profile favorable for widespread
drizzle. Latest models continue to support pockets of steadier
light rain within this moist ascent from central Oklahoma
southwest into the northern Rolling Plains. This justified
stretching the advisory eastward to Childress and Paducah.
Further south into the southern South Plains including Lubbock,
temperatures are slower to drop this evening and surface wet-bulb
temperatures remain closer to/but below freezing after midnight.
Expect an overall shorter window of combined subfreezing temps and
steady drizzle here with the majority developing after sunrise
when solar insolation can also aid in keeping exposed surfaces
closer to the melting point before air temperatures warm above
.PREV DISCUSSION... /issued 549 PM CST Thu Jan 12 2017/
Not much change from previous TAf with MVFR ceilings expected to
spread north this evening. With the edge of the stratocu already
within 100 nm have favored the faster onset at the terminals.
Increased low level moistening and isentropic ascent within the
lowest 3kft along with wet-bulb cooling at the surface should
yield areas of freezing drizzle as well later tonight. Light
freezing precip expected to continue through the morning Fri with
enough warming for phase change to liquid in the afternoon edging
in from the southwest. Though confidence is lower than normal on
the latter, elected to change to light rain at KLBB early
afternoon but kept freezing drizzle at other TAF sites. Wind
speeds will remain easterly around 10kt for the duration.
PREV DISCUSSION... /issued 340 PM CST Thu Jan 12 2017/
East-northeast winds have spread across the forecast area today and
temperatures have remained fairly flat since late morning. The cold
air near the surface will deepen tonight while isentropic lift will
be on the upswing. Forecast cross-sections show that a layer around
850 mb will begin to saturate this evening with moist advection over
the cold air. Low stratus will spread northwestward eventually
covering most if not all of the forecast area with overcast skies by
early Friday morning.
The coldest guidance has performed better so far today with this
shallow polar airmass, so we have followed it closely for
temperatures tonight and Friday. Lows tonight are expected to be
around freezing or a few degrees below expect for the southwest
South Plains, where temperatures may remain a few degrees warmer.
The airmass below 850 mb will initially be very dry, but will begin
to saturate due to cooling and moist advection. Around midnight or
so, we expect to see pockets of drizzle or light rain showers
develop first in the southern Rolling Plains then spread north and
west through the night and early Friday morning. The warm layer
centered around 850 mb looks to be pretty stout, with temperatures
as warm as 10 degrees c. However, the airmass between about 800 mb
and 400 mb is very dry. The shallow saturation should keep precip
amounts through the morning on the light side, while the warm nose
will have precip initially as liquid in that layer. However, with
surface temps near or slightly below freezing and some sub-cloud
evaporative cooling to consider, there is the potential for some
light icing Friday morning. Whether or not the ice will cause travel
issues will depend on just how cold the surface is and how much
precipitation falls (since it will be very light overall, ranging
from just a trace to maybe 2 or 3 hundredths). In general, the areas
of most concern will be from about Lubbock County to the north and
east - favoring the colder temperatures. At this time, we will hold
off on any advisories or other highlights as the confidence in
widespread ice developing on roads just isn`t there - however, this
could certainly change later on tonight if confidence increases in
Weak to moderate isentropic lift will continue across the forecast
area during the day Friday, continuing the chance of precipitation.
However, dry air about 800 mb will limit precipitation production.
Temperatures will remain cold but should warm above freezing across
at least western and southern areas in the afternoon. Freezing rain
or drizzle will remain a threat in the far southern Panhandle and
adjacent portions of the South Plains and Rolling Plains where we
anticipate temperatures will remain at or just under the freezing
Summary of changes: The greatest PoPs of 90-100 percent have
been confined to Sunday to reflect a continued slowing of the upper
cyclone`s track. We have also re-introduced some freezing rain on
Saturday morning over all but our far western zones, but otherwise
the forecast theme from recent days is still on track with a
continued preference for the colder NAM given its performance with
today`s cold front and temps in its wake.
Friday night opens with a steady uptick in moist isentropic ascent
as a 35-40 knot southerly LLJ transports much deeper Gulf moisture
poleward. Current feeling is that this advection component will be
most productive in generating precip near the remnant baroclinic
zone poised in a SW-NE fashion somewhere on the Caprock. Models also
keying on a 700 mb shortwave trough reaching this boundary toward
daybreak Saturday, so a window of stronger ascent should result with
some light-moderate rainfall. Temp-wise, we used a blend of our
prior forecasts with the 12Z 18Z NAM runs to establish freezing
temperatures over all but the western 2/3rds of our CWA late
Fri through Sat morning, but the overall marginality of these
values so close to or just below freezing could offer some relief
from steadier ice accumulations in moderate rainfall. If these temps
still look reasonable in later forecasts, then a freezing rain
advisory will be issued as both the coverage and rate of precip will
be more pronounced than Fri morning.
Temperatures are likely to warm to AOA freezing midday Saturday from
SW-NE as the shallow cold layer further modifies from precip and a
subtle deepening of the warm nose aloft, so further icing should
draw to a close as temps remain just warm enough Sat night and early
Sunday. As the much anticipated upper cyclone pivots northeast from
near El Paso on Sunday, stout 500 mb height falls on the order of 120
meters in 6 hours will spur the absolute best chances of rain CWA-
wide. Unseasonably rich PWATs AOA one inch will have no problem
being wrung out as the trough trends negatively tilted and centers
strong upper difluence squarely over the South Plains. Heavy
rainfall can be difficult to justify here in January, but with such
exceptional moisture and lift, the seasonal climatology simply does
not apply. On a similar note, SPC`s slight risk on Sunday is not
necessarily far fetched given the magnitude of forcing and
sufficient elevated CAPE of 500-700 J/kg which could yield some hail
with storms. However, this severe threat looks more focused
southeast of our FA near a warm front and comparably better
instability. Greatest threat on Sunday for us will certainly be
widespread heavy rains and an associated risk for some flooding.
Dry slotting then invades most of the region Sun night with some
signal for light deformation snow to catch our far W-NW counties
behind the departing upper low. This will also release a Cp airmass
through the CWA overnight on brisk northerly winds. Pattern
thereafter features additional trough energy reloading the broader
trough axis, but this focuses well to our SW with remoistening of
the dry slot looking unlikely. Else, seasonal temps should resume
Freezing Rain Advisory from 3 AM to 6 PM CST Friday for
Area Forecast Discussion
National Weather Service San Francisco Bay Area
411 PM PST Thu Jan 12 2017
.SYNOPSIS...Showers will end this evening with dry weather
expected for tomorrow at least through Monday. Overnight lows will
drop into the 30s in many spots with a few 20s even possible. Wet
weather with gusty southerly winds will likely return by the
middle of next week.
.DISCUSSION...As of 1:30 PM PST Thursday...A few showers remain
across our CWA this afternoon although they have generally been
confined to points south and east of SF Bay. Rainfall amounts and
rate have continued to diminish over the past few hours with many
places getting less than a tenth of an inch since mid-morning.
HRRR indicates a chance for showers at least into the evening
Temperatures have been chilly today with many locations running 5
to 10 degrees cooler than yesterday. At the same time, drier air
has filtered in which has dropped dew points 3 to 7 degrees. With
the combination of cooler and drier air, plus light winds
overnight and clear skies, temperatures should drop into the 30s
for most spots. Cannot rule out some upper 20s in sheltered valley
locations. The cold temperatures combine with recent precipitation
will possibly lead to black ice.
Once the rain ends this evening, computer models are in great
agreement that dry conditions will return to our entire region as
an area of high pressure builds to the coast. Only concern right
now will be another round of cold overnight lows going into
Saturday morning. In fact, that morning will likely be a few
degrees colder than tomorrow morning.
Rainfall will likely return in the Tuesday/Wednesday timeframe as
another Pacific storm system moves to the West Coast. Model timing
remains a bit off, however overall good agreement that widespread
rainfall will return for the middle of the week. Current guidance
indicates 2/3" to 1.5" for many urban spots with 2-4" for coastal
ranges. Southerly winds will also increase ahead of an associated
cold front. Lower elevation locations could see gusts over 40 mph
with higher elevation spots potentially gusting over 60 mph.
A second system is forecast to almost immediate follow and provide
another round of widespread rainfall. Right now neither system
appears as strong as the recent stormy weather we have had
although since it will be the fourth and firth round of active
weather, its impacts could still be quite substantial.
Needless to say, enjoy the break now and make all preparations before
the next round of active weather returns.
.AVIATION...As of 4:11 PM PST Thursday...For 00z tafs. Scattered
rain showers continue at this hour with solid coverage of mvfr
cigs. Shower activity and clouds expected to gradually decrease
and mix out overnight. Some concern for dense fog at ksts as light
winds develop overnight. As low drops over Socal tomorrow expect a
drier northeast flow with only partly cloudy skies.
Vicinity of KSFO....Some showers this evening gradually decreasing
overnight with skies expected to become vfr overnight and for the
start of Friday as well. Light NW winds.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...Some isolated showers this evening with
skies clearing overnight. Expect vfr skies for Friday.
.MARINE...as of 9:00 AM PST Thursday...Increasing northerly winds
will lead to hazardous conditions over the coastal waters with
numerous small craft advisories today and tonight. High pressure
builds off the coast Saturday and Sunday with decreasing winds.
Moderate swell will continue through tonight before decreasing
.Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pt Arena to Pt Reyes 0-10 nm until 9 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM
PUBLIC FORECAST: Bell
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Area Forecast Discussion
National Weather Service Norman OK
926 PM CST Thu Jan 12 2017
So far this evening, conditions have been changing more or less
as previously forecast. The available short-range forecast models
show conditions very similar to what we`ve been seeing for the
last day or two from the NAM, which remains the most believable of
As a result, we do not plan to make any changes to the forecast
.PREV DISCUSSION... /issued 541 PM CST Thu Jan 12 2017/
The 00Z aviation discussion follows....
Freezing rain, mainly light, is expected to develop late this
evening over southeast Okalhoma, then spread slowly northwest with
time. Initially, the freezing rain will likely be in the form of
scattered small showers. As the day progresses tomorrow, the
freezing rain will probably become more widespread, but will
continue to be showery...and generally fairly light. Ceilings
will lower this evening from southeast to northwest across
Oklahoma/north Texas, and we expect little change in ceiling
heights through the day tomorrow, with most of the area barely
MVFR (as opposed to IFR). The boundary between rain and freezing
rain will lie roughly along a line from KSPS to KADH, perhaps a
little farther north early Friday.
PREV DISCUSSION... /issued 427 PM CST Thu Jan 12 2017/
Around mid afternoon, temperatures ranged from the mid 30s across
northwestern Oklahoma to the lower 70s in far southeast parts
of the state. After sunset and overnight, temperatures will drop
below freezing north of a Shawnee to Lawton and Vernon, Texas
line and perhaps farther south.
As moisture increases above a shallow cold airmass, lower clouds
will develop and spread northward. NAM soundings suggest that by
midnight to 3 am...small convective showers may develop,
especially across the southern half of Oklahoma. Overall
confidence in this not high, but HRRR runs look somewhat
similar. Therefore, there is a risk of some light icing by
sunrise Friday, mainly within the Freezing Rain Advisory.
Weak isentropic ascent will continue through the day Friday
and this will result in mainly scattered areas of light freezing
rain and freezing drizzle. Mainly a cold rain is expected across
south central and southeast Oklahoma.
Although only light amounts of rain are expected during the day,
this may provide the best chance to create problem spots on roads,
especially bridges and overpasses.
Friday night into Saturday, isentropic lift will increase and
this will result in more widespread areas of freezing rain and
rain. This will also increase accumulations of ice on elevated
objects such as trees and power lines.
The temperature forecast and the risk of freezing rain and ice
becomes more uncertain during the day Saturday. The NAM was
followed closely for temperatures through Saturday night with a
slight decrease in temperatures across the northern half of
Oklahoma on Saturday. By late Saturday afternoon or early
evening, most areas along and south of Interstate 40 should be
above freezing. Farther north, freezing rain with embedded
thunderstorms should continue through at least early Sunday
morning. This will result in more ice accumulations and an
increased risk of power outages etc.
At this time, temperatures are expected to rise above freezing in
northern Oklahoma by at least Sunday afternoon.
A rather strong trough will move across west Texas and into the
central Plains Sunday into Monday. This will bring a period of
showers and thunderstorms, with a risk of heavy rainfall and
perhaps strong winds. There may be a risk of a few severe storms
across the southern part of the forecast area Sunday. We will try
and address this topic better in later forecast.
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 28 31 31 34 / 40 60 80 80
Hobart OK 28 30 30 32 / 30 50 70 80
Wichita Falls TX 33 34 33 37 / 40 60 70 70
Gage OK 23 27 27 31 / 10 30 60 80
Ponca City OK 26 30 29 31 / 20 70 70 80
Durant OK 38 45 38 43 / 40 60 70 60
OK...Ice Storm Warning from 6 AM Friday to 6 AM CST Sunday for
Freezing Rain Advisory until 6 AM CST Saturday for OKZ037.
Freezing Rain Advisory until 6 PM CST Saturday for OKZ021>030-
TX...Freezing Rain Advisory until 6 AM CST Saturday for TXZ083>085.
Area Forecast Discussion
National Weather Service Tulsa OK
953 PM CST Thu Jan 12 2017
Hourly temps have been handled fairly well by RAP forecasts and
the update did incorporate much of these trends. The exception
seems to be a nose of colder air pushing through a Siloam Springs
to Tahlequah zone and the updated forecast will lower these temps
and mention a fzra/ra mix accordingly.
KSRX VWP data support short term guidance of backing low level
winds atop the cold dome with associated upglide yielding an
expanding area of light convection. This trend will continue w/
the KFWS VWP data sampling the stronger low level flow which will
ultimately spreading northeastward allowing an increase in precip
further into the colder air. The updated forecast will also
increase tighten the precip amount gradient overnight to nearer
the 850mb boundary which slightly raises ice amounts tonight
across far NE OK.
Finally the idea of eroding the most shallow eastern portion of
the cold air beneath the strengthening warm advection is insisted
by the RAP but we have doubts. There is more likely to be a long
period of near steady temps for far E OK / NW AR while further
west temps will cool further. This warrants adding Okmulgee and
Wagoner cnty into the current advisory. Any further additions will
come as more real time data is seen. Beyond tonight the idea of an
expanding ice impact across areas north of I-44 still looks on
.PRELIMINARY POINT TEMPS/POPS...
TUL 32 34 32 37 / 60 70 80 80
FSM 44 52 43 54 / 70 50 60 40
MLC 35 47 37 47 / 60 60 80 50
BVO 29 32 31 34 / 30 70 80 80
FYV 38 49 43 51 / 70 60 70 60
BYV 33 40 39 48 / 70 70 70 60
MKO 36 45 37 44 / 60 70 80 60
MIO 30 36 32 36 / 50 70 80 80
F10 33 40 34 41 / 60 70 80 70
HHW 47 58 50 63 / 50 50 60 40
OK...Freezing Rain Advisory until noon CST Friday for OKZ057-058-
Freezing Rain Advisory from 6 PM Friday to noon CST Saturday for
Ice Storm Warning from 6 AM Friday to 6 AM CST Sunday for
AR...Freezing Rain Advisory until noon CST Friday for ARZ001-002.