Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/15/17
Area Forecast Discussion
National Weather Service Cheyenne WY
535 PM MDT Thu Sep 14 2017
.SHORT TERM...(This evening through Saturday)
Issued at 245 PM MDT Thu Sep 14 2017
Shortwave currently across southern Nevada is still progged to lift
rapidly northeastward through the night and be located over
northeast Wyoming by midday Friday. Increasing ascent ahead of it
will keep scattered to numerous showers and isolated tstms going
through much of the night. Cannot rule out an isolated storm with
small hail, however the threat looks rather small with limited
instability. The coverage of showers will generally decrease into
sunrise Friday in the subsidence behind the shortwave trough. West
winds will become breezy for areas near and west of the Laramie
Range by Friday morning at the 850mb CAG-CPR gradient increases to
around 40 meters.
There will be an overall lull in precip during the day on Friday,
except across far northwestern zones. Main upper trough will move
across Wyoming on Saturday, with the associated sfc fropa on Friday
aftn/evening. Upper level divergence will be on the increase by
late Friday evening into Friday night, with higher PoPs spreading
over the plains. Snow levels will drop to around 10000 ft by
Saturday morning, so could see 1-3 inches in the higher peaks of the
Sierra Madre and Snowy Ranges. Saturday`s highs will be some of the
coolest we have seen in quite a while, with most locations
struggling to get above the mid 60s. Shower chances will decrease
after 18Z Saturday in the wake of the upper trough.
.LONG TERM...(Saturday night through Thursday)
Issued at 245 PM MDT Thu Sep 14 2017
Warmer temperatures seen for the CWA Sunday and Monday as the area
will be in between systems with the next upper trough digging into
the Pacific northwest by late Monday. One shortwave may bring some
showers to the plains Sunday evening otherwise dry weather expected.
Cooler and wetter conditions then arrive across the CWA in the
Tuesday through Thursday time period as the upper trough amplifies
over the western CONUS and a cold front pushes across the CWA late
Tuesday. Most widespread rain should be later Weds into Thursday
as a shortwave lifts across the region.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 532 PM MDT Thu Sep 14 2017
Main concern tonight will be IFR/LIFR possibilities across the
northern Panhandle over into east/central Wyoming. Latest HRRR
showing a northeast cold front dropping into this area after 06Z
with upsloping northeasterly winds. Did bring KCDR down to IFR
with it extending over to KLSK and maybe KDGW. KAIA may get into
this towards 12Z Friday. WIll wait to see what the trends are
later this evening. Otherwise, showers and isolated thunderstorms
possible across our southeast Wyoming airports this evening. Then
windy most of the day Friday.
&&
.FIRE WEATHER...
Issued at 245 PM MDT Thu Sep 14 2017
No fire weather concerns through the weekend. Cooler temperatures
will occur on Friday and Saturday with minimum afternoon humidity
values remaining above 25 percent. There will be a good chance of
showers across much of the region from this evening through Saturday
morning.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
SHORT TERM...ZF
LONG TERM...RE
AVIATION...GCC
FIRE WEATHER...ZF
Area Forecast Discussion
National Weather Service Duluth MN
1035 PM CDT Thu Sep 14 2017
.UPDATE...
Issued at 1027 PM CDT Thu Sep 14 2017
A dangerous flooding threat is developing across portions of the
Northland this evening as thunderstorms continue to develop and
track across the area. The strongest storms producing the most
significant rainfall extended from western Cass County east
northeast through the Iron Range and toward Lutsen. Radar and
observations show 2 to 5 inches of rainfall in the Zim, Makinen,
Skibo, and Whyte areas. More rain is on the way and another 1 to
3 inches could occur through 1 am. Significant flooding will be
possible in those areas.
We shifted higher chances for showers/storms further south as the
line of storms has been sagging south with time along with the low
level boundary. Strong FGEN forcing is forecast through much of
the night and there is a pool of unstable air over much of the
region. A strong low level jet is also in place but it will shift
east with time tonight. A shortwave was moving through as well
and there could be a diminishing trend late tonight as the jet
diminishes and weak subsidence behind the shortwave occur.
UPDATE Issued at 633 PM CDT Thu Sep 14 2017
Strong to severe thunderstorms continued across portions of
northeast Minnesota with additional showers and storms continuing
to form west to the North Dakota border. Strong low level FGEN is
present and will be through much of tonight and a low level jet
will be strengthening this evening but should then shift east more
into northern Wisconsin later tonight. We think showers and
storms will continue through much of tonight, especially over
northern Minnesota. There will be a threat for very heavy rain. A
report just west of Crane Lake was around 2.5 inches of rain as of
530 pm. We will be issuing a Flash Flood Watch for much of far
north to northeast Minnesota through 11Z to account for the
possible heavy rainfall.
&&
.SHORT TERM...(This evening through Friday)
Issued at 311 PM CDT Thu Sep 14 2017
Increasing chances of showers and thunderstorms will occur this
evening as a more active weather pattern sets up across the region.
A mid-level shortwave trough, along with enhanced 850-700 mb layer
frontogenetical forcing, will act as the mechanism for these showers
and storms. The environment should be capped in some locations,
given values of MLCIN in the 50 to 150 J/kg range. However,
there`s plenty of elevated instability, with MUCAPE values from
the 14.12z GFS/CMC/NAM models between 1000 to 2000 J/kg, so if
storms can break through the capping inversion, there is plenty of
instability for them to tap into. The HRRR model is indicating
some stronger convective cells out ahead of the leading wave, so
that will need to be watched from 23z this afternoon onward. So
far this afternoon, we`ve issued a few SPSs due to a single strong
thunderstorm that developed over northwest Minnesota and
translated east-northeastward over Koochiching county. However, it
appears to be struggling to sustain its updraft despite the
amount of instability in the region. Heavy rainfall is possible
with some of these storms, given Pwat values between 1.3 and 1.6"
tonight.
Along with the chances of showers and storms tonight, areas of fog
is expected to develop due to on-shore flow tonight, along with
low condensation pressure deficits and light winds. Fog is
expected to begin along Lake Superior, and build further inland as
the night goes on. Most of the heavy rainfall is expected over the
Iron Range eastward into the Minnesota Arrowhead regions. Chances
of thunderstorms should decrease after midnight due to the loss
of favorable instability. The respite from storms will be short-
lived as another round of showers and storms are expected again
Friday as another shortwave trough moves into the region. The
convective-allowing models are struggling to resolve the activity
for Friday, as the NAMNest model is more active than the WRF
NMM/ARW models, which are going drier. While uncertainty does
exist, the synoptic models are showing decent agreement on
precipitation chances around the forecast area. Chances of
thunderstorms will increase Friday afternoon as better
destabilization builds. A strong baroclinic zone will remain over
the region given more southerly winds over northwest Wisconsin and
more northerly winds along the International Border. High
temperatures Friday will range from the upper 50s and lower 60s
north to the middle to upper 70s south, with some lower 80s also
possible.
.LONG TERM...(Friday night through Thursday)
Issued at 254 PM CDT Thu Sep 14 2017
The Northland will begin the period with cool, easterly low level
flow, and warm and humid southwest flow aloft. An area of low
pressure will be in the Central Plains Friday evening. Much cooler
wrap around air will be in western North Dakota and in Canada,
waiting to swing into the Northland once the Central Plains low
moves through the region. Passing shortwaves and the strong nocturnal
low-level jet could trigger showers and thunderstorms across the
Northland Friday night, while the Central Plains low lifts to
northern MN.
The low will continue to move through northern MN Saturday, lifting
into Ontario Saturday night. It`s cold front will slowly work its
way eastward across northern MN Saturday, then rapidly swing through
the Northland Saturday night when a deep upper-level low lifts into
the Northern Plains and south-central Canada. The Northland could
get showers and thunderstorms Saturday and Saturday night. A few
storms could be strong, capable of small hail and heavy rain.
People across the Northland may wake up to what feels like fall on
Sunday. Much cooler air will move into the region amid the westerly
flow in the wake of the cold front. Expect a cool and breezy day.
Concerned models may be too warm, but stuck with model consensus for
now. We might cool the forecast with time. Cloud cover will play a
part. Most models think it will be mostly sunny, but the residual
moisture from the previous day, combined with the very cold air,
might trigger broken cumulus in the afternoon, which would limit
heating. The forecast for now is for highs in the upper 50s to lower
60s.
Southerly flow will redevelop Monday and bring back warmer air into
the region into the middle of the week. The moisture return will
also increase the chances of showers and storms. The GFS has much
more robust precipitation than the European. The best chances will
likely be when the cold front swings through during the middle of
the week, but the GFS has this occurring significantly sooner than
the European and Canadian.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 633 PM CDT Thu Sep 14 2017
A stalled frontal boundary and low level FGEN has led to showers
and strong to severe thunderstorms over northern Minnesota this
afternoon and early evening. The showers/storms will continue
overnight as the strong FGEN forcing is forecast through the
night. Ceilings will lower for most areas overnight along with fog
developing. IFR/MVFR conditions will expand, especially over
northern Minnesota and they will continue into Friday. An area of
low pressure will then move toward the region on Friday producing
more showers/storms and IFR/MVFR conditions.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 59 67 57 72 / 70 50 60 40
INL 53 59 53 63 / 60 80 80 50
BRD 61 75 62 69 / 30 60 60 50
HYR 63 80 63 79 / 20 30 40 30
ASX 59 74 60 78 / 40 30 40 40
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Flash Flood Watch until 6 AM CDT Friday for MNZ010>012-018>021-
025-026.
LS...Small Craft Advisory until 10 PM CDT Friday for LSZ144-145.
&&
$$
UPDATE...Melde
SHORT TERM...JTS
LONG TERM...Grochocinski
AVIATION...Melde
Area Forecast Discussion
National Weather Service Green Bay WI
1044 PM CDT Thu Sep 14 2017
Updated aviation portion for 06Z TAF issuance
.SHORT TERM...Tonight and Friday
Issued at 214 PM CDT Thu Sep 14 2017
Due to a little more mixing, fog along the Lake Michigan shore
has finally lifted to a stratus deck, moved to the open waters or
diminished a bit. Forecast challenge for tonight then focuses on
low temps and fog potential again. Shower and storm potential
over Northwest Wisconsin is on the increase through Friday.
With a bit more mixing expected with the increasing south gradient
tonight into Friday, anticipate less fog in terms of coverage and
duration. But still anticipate some fog development in the rivers
basin areas and low lying areas. Fog has been persistent over Lake
Michigan the last few nights as well and patchy fog is possible
again overnight.
Post frontal scattered storms and showers were developing over
far Northwest Minnesota into North Dakota. The Convection was
also in a better sheared region with slightly higher PWATs. The
GFS and ECMWF were more aggressive with convection reaching the
DLH area by 4 pm this afternoon vs the drier NAM model. Due to
initialization, will run with the drier NAM tonight into Friday
and begin to bring in chances for convection Friday afternoon
across far North Central Wisconsin. The HRRR was also dry this
afternoon into tonight for far NW Wisconsin. Mid level lapse
rates are on the increase over Minnesota and far Northwest
wisconsin this afternoon, but plenty of dry air to overcome per
MSP raob this morning.
.LONG TERM...Friday Night Through Thursday
Issued at 214 PM CDT Thu Sep 14 2017
At the start of the period a few models continue to show a brief
opportunity for showers and perhaps some thunder in the far north
Friday evening. However, latest runs are trending towards keeping
the pcpn just north of Wisconsin. Kept slight chance mention in
far north- central Wisconsin, mainly Vilas and northern Oneida and
Forest Counties. Otherwise, the rest of the area to remain dry
Friday evening through Saturday afternoon.
A mid-level short wave begins pushing the surface cold front
southeast Saturday evening through Sunday afternoon. As the front
progresses expect to see the chance for showers and thunderstorms
move from NW to SE across the forecast area. Severe potential
appears minimal at this point. Stronger storm development looks
more likely to the west Saturday afternoon and evening when
instability will be greater. Weakening instability into the night
would suggest limited severe potential.
GFS, ECMWF, and Canadian still trying to come to a consensus on
the large scale pattern heading into next week. There seems to be
better agreement that surface high pressure and weak mid- level
ridging will keep the forecast area dry on Monday. Beyond that
differences persist. EC is still deepening the trough across the
western CONUS which allows a ridge to build across the western
Great Lakes region through the week. The GFS solution depicts a
broader trough in the west and the ridge developing much further
east, which puts us in a southwest flow pattern with opportunities
for multiple shortwaves to bring chances for showers and
thunderstorms. The Canadian is somewhere in between. Forecast
continues to features on/off chances for showers and thunderstorms
from Tuesday and beyond. It`s too early to determine if severe
storms would be a consideration at this point.
Temperatures will be well above normal on Saturday, cool off some
Sunday/Monday following the cold front (but still above normal),
and then return to highs in the low to middle 70s for the middle
of the week. Expect cooler highs along Lake Michigan most days.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 1037 PM CDT Thu Sep 14 2017
A few thunderstorms have developed over northwest Wisconsin this
evening. The airmass is considerably more stable over north-
central WI, so they may diminish before reaching Rhinelander. But
added a vcsh for a couple hours after midnight in case a shower
survives the trip. Otherwise, not expecting fog to be much of an
issue tonight, except for near the lakeshore possibly. Mainly
quiet weather for Friday into Friday night, with breezy south
winds.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM.....TDH
LONG TERM......KLB
AVIATION.......MPC
Area Forecast Discussion
National Weather Service Norman OK
1053 PM CDT Thu Sep 14 2017
.DISCUSSION...
&&
.AVIATION...
VFR conditions are expected to continue until 160600. South winds
will become gusty after sunrise across nearly all terminals.
&&
.PREV DISCUSSION... /issued 911 PM CDT Thu Sep 14 2017/
DISCUSSION...
Elevated showers and thunderstorms over the Texas Panhandle have
weakened into patches of light rain. The higher MUCAPE values east
of the Panhandles, along with a strengthening LLJ, raise some
concern for redevelopment, possibly before midnight. As a result,
we have introduced 20% rain/storm chances in far western Oklahoma
a couple of hours earlier than the previous forecast...in case the
showers/storms do redevelop.
Otherwise, the forecast looks good, and no other changes are
planned for this evening.
CmS
PREV DISCUSSION... /issued 706 PM CDT Thu Sep 14 2017/
DISCUSSION...
AVIATION...
VFR conditions will continue through Friday. Gusty south winds
will develop at most terminals by late morning Friday.
PREV DISCUSSION... /issued 350 PM CDT Thu Sep 14 2017/
DISCUSSION...
Midlevel moisture/cloudiness is expected to be on the increase
tonight into tomorrow across northwest Oklahoma. The moisture may
interact with elevated forcing in marginally unstable air to
produce some isolated showers and weak thunderstorms for tonight
across our northwestern CWA. The latest HRRR & NSSL WRF models
keeps any convection limited across the Texas/Oklahoma
panhandles, although the Texas Tech WRF hints a few storms
possible into our northwest well after midnight. I will keep POPs
low but in for tonight across the aforementioned area. For
Friday, daytime heating/vertical mixing in the boundary layer will
keep winds gusty across our area, while South winds will continue
to bring in unseasonably warmer air with temperatures well in the
lower to mid 90s. The winds, warm temperatures, and RH values in
the lower 30s will maintain elevated fire weather conditons for
Friday as well.
A deepening trough of low pressure across the Western U.S. will
bring a sfc boundary across the central high plains, bringing in
low chances for another round of isolated showers and
thunderstorms possible for this weekend. Right now, the chance are
limited to northwest Oklahoma for Saturday, then push into central
and southwest Oklahoma for Sunday. However model guidance is in
better agreeance for Sunday, although ECMWF is a little bit wetter
at this point.
For next week, remnants of a tropical system currently in the
Pacific may bring in our next chance for rain, mainly on Tuesday
into Wednesday. The latest GFS run continues to be wet, and brings
in the remnants of current tropical storm Norma across old Mexico
and into the southern plains. However, the ECMWF continues its
trend of upper ridging during that time period. Because of the
uncertainty and time out, will keep POPS low for Tuesday and
Wednesday.
&&
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 70 91 72 90 / 0 10 10 0
Hobart OK 71 94 71 92 / 10 20 10 10
Wichita Falls TX 71 95 73 93 / 0 10 10 0
Gage OK 70 94 68 93 / 20 20 20 20
Ponca City OK 70 93 72 91 / 10 10 20 10
Durant OK 69 88 71 90 / 0 0 0 0
&&
.OUN WATCHES/WARNINGS/ADVISORIES...
OK...None.
TX...None.
&&
$$
23/09/09
Area Forecast Discussion
National Weather Service Blacksburg VA
1117 PM EDT Thu Sep 14 2017
.SYNOPSIS...
High pressure will build over the Mid Atlantic region tonight
and cover much of the eastern United States through Sunday. A
cold front will approach the region from the northwest on Monday
and Tuesday. A gradually warming trend to slightly above normal
temperatures is expected through the middle of next week.
&&
.NEAR TERM /THROUGH FRIDAY/...
As of 1113 PM EDT Thursday...
Due to less cloud cover over southwest Virginia into the NC
foothills, appears fog will become a little more favorable in
forming. Anticipate that skies will clear enough to allow patchy
fog at most locations overnight, but not enough for a dense fog
advisory at the moment, but will have to monitor. No other major
changes to the forecast were made with this update, as showers
over southside VA/NW NC piedmont, weaken and lift northeast by
3am.
Previous discussion from early evening...
Still a considerable amount of cloudiness around across the
region. Noting some increased shower development from south of
Lynchburg into Southside VA and the north- central NC Piedmont,
forced by weak convergence along with dewpoints in the mid 60s
and some breaks in stubborn overcast. Good agreement from the
12z WRF NMM, 21z HRRR and 18z 3-km NAM in progressing these
showers northeastward and dissipating fairly early tonight (~
02z). Surface ridge should begin to build in later tonight.
While it`s unlikely skies fully clear out especially in the
western Appalachians in WV, shallow but rather stout inversion
depicted in BUFKIT soundings should allow for patchy mist or
light ground fog to develop in cloud breaks after midnight. Lows
mid 50s to lower 60s appear on track with no alterations needed
there.
Previous near-term discussion issued at 310 PM Thursday
follows...
Surface high pressure builds over the region tonight and
Friday. No organized lift or forcing this time and winds are to
weak to contribute with any upslope component. This will limit
the best probability of precipitation to the afternoon and
evening. Even with daytime heating, there will not be much
instability on Friday.
Bufkit forecast soundings for Friday morning showing shallow,
but strong surface based inversion favoring fog. Still question
the extent and timing of fog formation with at the cloud cover
but will hold it in the overnight forecast for now. Models move
deeper moisture to the northeast tonight then hold moisture in
below 850MB with sporadic breaks. Will stay close to guidance
for temperatures.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 310 PM EDT Thursday...
High pressure remain over much of the eastern United States
through Sunday. Saturday night and Sunday surface and low level
wind turn to the northeast with slightly increasing winds speeds
between the high and Tropical Storm Jose. Expecting broad upper
ridging over the eastern United States Friday night through
Sunday with 850MB temperatures gradually warming from around +12
to +16.
Similar weather pattern continues through Sunday with little to
trigger any precipitation. Guidance reasonable for temperatures
through the period.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 200 PM EDT Thursday...
This portion of the forecast will be characterized by limited
chances of precipitation and little deviation of temperatures from
day to day, with these readings averaging five to eight degrees
above normal.
The best, perhaps only, chance of precipitation during this
timeframe will be on Monday. We will be watching a cold front
approach the area from the west. While guidance is fairly uniform
with this feature reaching the area, it is also fairly uniform with
our area within a subsidence zone, on the northwest side of
Hurricane Jose, as it potentially tracks north, east of the east
coast of the U.S. So what precipitation the front brings with it
will be squelched by first limited moisture, and increasing local
subsidence. The forecast will reflect isolated showers through the
day, with isolated showers and storms in the afternoon, with the
focus across the mountains.
Sunday night through early Thursday, both surface high pressure, and
a building ridge aloft will minimize precipitation chances, and
provide for more sun than clouds.
Thursday, we will be watching another cold front approach from the
west. Guidance among the models is not as uniform with this feature
as it is with the Monday feature. Will allow for isolated coverage
across the mountains for showers, but confidence is lower than that
of Monday.
During the period, low temperatures will range from the mid to upper
50s across the mountains and around 60 to the lower 60s across the
Piedmont. High temperatures will range from the mid to upper 70s
across the mountains with readings around 80 to the lower 80s across
the Piedmont.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
As of 715 PM EDT Thursday...
Regional radar mosaic shows isolated showers east of the Blue
Ridge from just south of Lynchburg into the NC Piedmont. These
showers may impact Danville in the next couple of hours before
dissipating by 02z. Otherwise, multi-layered BKN/OVC VFR/MVFR
ceilings should predominate through most of the overnight hours
across the terminals. Low-level moisture should remain trapped
and with some potential cloud breaks late, could see a fair
amount of MVFR mist. Indicated temporary LIFR fog before
sunrise where feel best shot at some breaks are but confidence
is no better than medium on this.
Should continue to see MVFR ceilings at Bluefield and Lewisburg
until mid-morning Friday, but presence of cool pool aloft
should allow for SCT/BKN VFR cumulus to re-develop elsewhere.
May even see an unrestricted diurnal shower from these but
confidence in impact to specific airports was too low to place
in the TAFs attm.
Winds through the period are light/variable to calm as surface
ridge builds into the region tonight and into Friday.
Extended Aviation Discussion...
Any isolated diurnal showers Friday should dissipate early
Friday evening. Some MVFR showers are possible on Saturday with
another short wave. The chance of precipitation remains low for
Sunday and Monday. Expect diurnal isolated showers and
thunderstorms across the terrain. Aside from valley fog in the
early morning, conditions overall should be VFR. Tuesday may
feature some isolated MVFR showers in the mountains.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
$$
SYNOPSIS...AMS
NEAR TERM...AL/AMS/WP
SHORT TERM...AMS
LONG TERM...DS
AVIATION...AL/AMS
Area Forecast Discussion
National Weather Service Seattle WA
849 PM PDT Thu Sep 14 2017
.SYNOPSIS...High pressure and northerly flow will maintain dry
conditions with near or slightly above average temperatures through
Saturday. Rain will return to the area Sunday and continue into
Monday, as a low pressure system moves into the region. A lingering
trough will keep a chance of light showers in the forecast through
mid week.
&&
.SHORT TERM...An upper level ridge will continue to bring dry,
northerly flow to the area tonight and Friday. Expect mostly clear
skies and temperatures near normal. Wildfire smoke, as seen on the
visible satellite, has been drifting west again, especially from
the fires near Mount Rainier. The HRRR model keeps most of the
smoke in the central Cascades in Pierce and Lewis counties through
Friday. The ridge weakens somewhat as we move into Saturday but
we are still looking at dry and mild conditions.
A pattern change to moist SW flow is anticipated on Sunday. By
then a stronger/wetter front will shift inland for a period of
wet weather. We should see widespread measurable rain across the
region. Temperatures will also trend down with highs mainly in the
low-mid 60s. 33
.LONG TERM...Previous discussion...A broad upper low closed off
over the Pacific Northwest will produce widespread showers Monday.
Colder air aloft will arrive with snow levels falling as low as
5000 to 6000 ft. Some light snow accumulation could fall in the
higher mountains. Depending on whether we get some sunbreaks,
diurnal instability could be just enough to pop a couple of
thunderstorms. At this point, any lightning looks very isolated
with no particular area favored. Will leave out of the forecast
for now but at some point it may be worth adding an isolated
mention.
The low shifts east of Tuesday, but another system arrives in
northwest flow. Rain or showers should develop again Tuesday and
slowly taper off Wednesday. Highs early next week will struggle to
reach the low 60s.
By late Wednesday and Thursday, the GFS and ECMWF differ on the
chance of precipitation. The GFS is slower, showing some lingering
threat of spotty showers into Thursday. A ridge is shown to move the
area by the ECMWF with dry conditions. Left some low chance pops or
slight chance wording in the forecast but it could end up being a
dry day. Mercer
&&
.AVIATION...Dry northerly flow aloft with weak low level onshore
flow will continue through Friday. The air mass remains generally
dry and stable. The exception is patchy low clouds and fog along the
coast in the marine layer tonight.
KSEA...VFR conditions with northerly winds 3 to 6 kt.
&&
.MARINE...Weak low level onshore tonight will continue through
Friday. A small craft advisory for northwesterlies over the coastal
waters remains in effect until 11 PM PDT this evening. Winds will
generally ease after midnight. Low level offshore flow will develop
on Saturday ahead of a weather system approaching the coastal
waters. A strong front will move through area waters Sunday and
Monday, bringing at least small craft advisory strength winds to
most waters. Gale force winds are possible on the coast.
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory until 11 PM PDT this evening for Coastal
Waters From Cape Flattery To James Island 10 To 60 Nm-
Coastal Waters From James Island To Point Grenville 10 To
60 Nm-Coastal Waters From James Island To Point Grenville
Out 10 Nm-Coastal Waters From Point Grenville To Cape
Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville
To Cape Shoalwater Out 10 Nm.
&&
$$
www.weather.gov/seattle
You can see an illustrated version of this discussion at
www.wrh.noaa.gov/sew/gafd/latest_webafd.html
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
832 PM EDT Thu Sep 14 2017
.UPDATE...
00Z water vapor and H4 RAP analysis shows the Florida
peninsula within a zone of deep southwesterly flow between
mid/upper level ridging to the east and south of the
peninsula...and troughing extending south from the lower MS
valley into the western/central Gulf of Mexico.
At the surface...weak high pressure extends from the
western Atlantic to the Florida peninsula...putting us on
the western periphery of this ridge. Off to our west we find
an inverted trough over the central Gulf associated with the
parent troughing aloft. As of 00Z we still have plenty of
diurnally driven showers/storms over the peninsula...with
the bulk of the activity within our forecast zone now south
of the I-4 corridor. This activity can be expected to
persist for another couple of hours before dissipating with
the loss of diurnal heating.
Offshore we see another batch of showers/storms that is
being driving by the combination of mid/upper level forcing
on the eastern side of the upper trough over the Gulf and
the surface focus related to the surface reflection trough
in the lower levels. This area of rain has been migrating
toward the FL west coast, however NWP is in good agreement
of a rapid weakening trend as it gets closer to the coast
and becomes removed from the large-scale forcing. Am
trusting in the NWP ensemble solution at this point and
allow PoPs to taper off over land in the next couple of
hours. However, should this area of rain not behave as
expected, some changes to the overnight forecast will be
required...especially for the coastal counties. Hopefully
this will not be necessary. We do not need the rain at this
point.
Assuming, the forecast works out...drier conditions region-
wide can be expected for the second half of the
overnight...into the morning hours of Friday. Things will
however likely change during the afternoon...especially
later afternoon/early evening hours. Deep moisture will be
in place over the region on Friday...so no real negative
thermodynamic aspects of the column to limit diurnal
convection. At the same time...the surface ridge axis will
shift a bit to the north...allowing a more defined east to
west synoptic flow in the lower levels. This easterly flow
is favored for sea-breeze focus/convergence and enhanced
updrafts along the I-75 corridor of the state...and expect
this to be true on Friday. Sct-nmrs showers and storms are
in the forecast for the second half of the day. The summer
weather pattern is not quite over yet folks.
&&
.AVIATION (15/00z through 16/00Z)...
An active evening of thunderstorms ongoing in the vicinity
of KPGD/KFMY/KRSW. Keep tempo groups for storms in through
02Z...and then taper things off. Further north...storms have
exited the terminals...but watching an area of
showers/storms offshore slowly approaching the coast.
Guidance is in agreement showing this area dissipating
before reaching the coast, but will need to monitor closely.
Otherwise...prevailing VFR conditions expected for all
terminals after 02Z for the overnight and morning hours of
Friday. Another active afternoon/evening in terms of
thunderstorms anticipated for all terminals Friday.
&&
.Preliminary Point Temps/PoPs...
TPA 77 91 76 89 / 20 60 40 30
FMY 76 92 75 91 / 50 40 20 20
GIF 74 91 74 91 / 40 50 20 40
SRQ 76 89 76 88 / 20 50 40 20
BKV 74 90 74 90 / 20 60 20 40
SPG 78 90 77 89 / 20 50 40 30
&&
.TBW WATCHES/WARNINGS/ADVISORIES...
FL...None.
Gulf waters...None.
&&
$$
UPDATE/AVIATION...14/Mroczka