Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/04/24
Area Forecast Discussion
National Weather Service La Crosse WI
556 PM CST Tue Dec 3 2024
.KEY MESSAGES...
- VERY WINDY Wed afternoon-evening. Wind Advisory for most locations
west of the Mississippi river (could be expanded east). Wind gusts
35 to 45 mph for entire area with sustained from 20 to 30 mph. Winds
WILL impact travel and blow lightweight objects around (holiday
decorations).
- BITTER COLD start to Thu with combination of wind and cold air
producing 5 to 15 below wind chills. Bundle up for your commute to
work/school.
- SCATTERED SNOW SHOWERS Wed (20-50%). Accumulations look minimal at
this time, but could provide further travel impacts with sudden
reductions in visibility, some slick spots on roads.
- Cold is short-lived with above normal air moving in for the
weekend - back in the 40s for some!
&&
.DISCUSSION...
Issued at 215 PM CST Tue Dec 3 2024
- WED/THU MORNING: windy, colder and low end snow shower chances (20-
50%)
OVERVIEW: upper level shortwave trough still on track to drop
southeast out of Canada tonight, digging across the great lakes Wed
night, developing a negative tilt as it drives over the new england
states by thu evening. Although the associated sfc low will hold
across southern Canada, a couple related sfc fronts will move across
the region. Very strong cold air advection, some low level
instability, and tightening pressure gradient accompany the system,
promising strong/gusty winds, much colder air, and some snow shower
chances. The bulk of its impacts will be shifting east with the
storm Thu morning.
WINDS: a lot of elements progged to come together and foster a very
windy period for the region with Wed afternoon-evening likely
harboring the strongest gusts for the local area.
1) Tightening sfc pressure gradient
2) Unidirectional winds (northwest) through nearly the entire column
Wed aft/eve.
3) Mixing upwards of 825 mb with RAP/HRRR/NAM/GFS bufkit soundings
suggesting upper 30s to around 40 kts will be brought to the sfc for
the afternoon/early evening Wed.
4) Trop fold could bring even stronger winds surfaceward, with the
1.5 PV sfc reaching 750-800 mb in the NAM/GFS, but as low as 850 mb
in the EC. The EC has been the most robust with this.
All this has been a very consistent signal in the models the past
several days. The EC (as already alluded to) has been the most
bullish on strong winds. Essentially 100% of its ensemble members
paint 40 mph gusts for the entire forecast area for Wed aft/eve. In
its 03.12z run, 20 of the EPS members suggest 50+ mph could be
attained Wed afternoon at KRST. In addition, 03.00z EFIs are
0.8+...an increase over already high values from previous runs
(0.7+). The EC is "all in" for a high wind event, perhaps too much
as it is running at the top end of the guidance. That said, ample
support from the other short/medium range guidance that 45 mph gusts
could be reached, along with periods of sustained 30 mph.
Per coordination with surrounding offices, will issue a Wind
Advisory for most of SE MN/NE IA for 18z Wed through 03z Fri. May
need to expand this eastward - and will let further model updates,
realtime observations, steer that need.
Eitherway, it will be a very windy day Wed/Wed night. In addition,
with how cold it is expected to get, any potential loss of power due
to strong winds will have added impacts on heating. Prepare
accordingly.
TEMPS: don`t expect much drop in temps from the early evening
through the overnight as the southerly fetch/low level warming
persists. Much colder air starts to return after 12z Wed, in earnest
post the second front. Highs for most will be by noon, with steady
or falling through the afternoon. 850 mb temp anomalies via the
NAEFS and ECMWF are around -2.5 for Wed night while determinist runs
of the EC/GFS 850 mb temps fall from near 0 at 12z Wed to -15 C by
12z Thu. The Grand Ensemble places a 80-100% for single digit lows
west of the Mississippi River Thu morning with less chances north of
I-94 where clouds could be more prevalent. Add in the strong
northwest winds and wind chills from -5 to -15 should be planned
for. Bundle up early morning commuters to work/school Thu.
PCPN CHANCES: a variety of lifting mechanisms will provide multiple
means to force snow showers Wed into Wed evening. A loft, the upper
level trough drops southeast across WI with mostly mid/upper level
QG convergence with it. At the sfc, while the system`s associated
low will be tracking west-east just north of Great Lakes, 2 cold
fronts will stretch south/southwest of the low. The first is progged
to slide southeast across the region in the early morning hours (12-
15). The second takes a similar track during the afternoon. Strong
cold air advection in the low levels will promote 1000:850 mb lapse
rates of +9 C/km (mostly behind the second front). Meanwhile
RAP/HRRR Bufkit soundings depict weak instability through the day.
Same soundings point to enough saturation to form clouds/showers.
While there is initially weak, disjointed low level Fgen along both
sfc fronts, CAMS modeled reflectivity depicts mostly cloud
streets/convection parallel to the mean wind (not in relation to the
frontal lift). RAP does become more organized and increases the low
level Fgen as the second front shifts southeast of the local area,
so perhaps frontal orientated convection would increase then.
Short term guidance is low with its snow chances - perhaps more
reflective of their low QPF output. The forcing, however, says
chances should be higher. Will increase above the model blend with
this in mind. Where snow falls, amounts do look relatively minor.
That said, if parallel bands do form, very localized snow could drop
for a longer period of time - and thus, higher amounts could be
realized. A lot of "ifs" here, but its a scenario to monitor.
- WEEKEND: warming up!
Change in the upper level pattern moving into the weekend with the
zonal/broad ridging taking over. Latest deterministic runs have 850
mb temps climbing from the teens below zero at 12z Thu to the single
digits above for Sat-Mon. High temps in EPS suite of ensemble
members have placed 75% of its members in the low/mid 40s for highs
Sun, just a few degrees cooler either side of that day. A very
consistent signal in the EPS. The GEFS has been cooler than the EPS,
but has shown some increase over its past few runs. Either way, all
trends point to at/above normal temps moving in for the weekend and
the start of the new work week.
The change in the pattern could allow for bits of shortwave energy
to spin near/across the region. Current outlay of the ensembles
suggest the higher pcpn probabilities would lie north/south of the
forecast area.
&&
.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 552 PM CST Tue Dec 3 2024
We are looking at VFR conditions with southerly winds between 10
and 15 knots for tonight. In the wake of a strong cold front on
Wednesday morning, winds will shift to the northwest. Sustained
winds will be 20 to 30 knots with gusts of 30 to 45 knots. In
addition to the strong winds, there will be MVFR ceilings.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Wind Advisory from noon to 9 PM CST Wednesday for MNZ079-086-
087-094-095.
IA...Wind Advisory from noon to 9 PM CST Wednesday for IAZ008>010-
018-019-029.
&&
$$
DISCUSSION...Rieck
AVIATION...Boyne
Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
713 PM CST Tue Dec 3 2024
...New UPDATE, AVIATION, MARINE...
.UPDATE...
Issued at 654 PM CST Tue Dec 3 2024
Interesting evening underway, as weak surface low pressure
(inverted trough) was hugging the coast with a sharp wind shift
between Bayview/South Padre and Brownsville. That same wind shift
showed a sharp difference in temperatures, from the low to mid 70s
on the coast where east winds continued, to the low to mid 60s in
the Brownsville/Harlingen area...and around 60 in the mid Valley
and upper 50s across the Brush Country. Bands of overrunning rain
continued to roll across eastern Cameron County (especially),
where daily totals were nearing 2 inches (1.8" unofficially) at
Brownsville/South Padre Int`l Airport.
The trough has also cranked up seas and swells above originally
forecast, and web cams showed both rough/high/confused surf but
also run-up toward the dune line just before sunset. Based on
local guidance for the incoming swell as well as adjusted model
forecast tide levels, have hoisted a Coastal Flood Advisory to
continue through pre-dawn Wednesday. Tides may begin to run out a
little sooner...but elected to add a buffer of around 6 hours
after high tide (859 PM) based on the expected incoming easterly
swell which may keep a prolonged buffer of water to or just into
the dunes.
Based on the surf and swells, hoisted a high surf advisory for the
overnight. While unlikely that many will be venturing into the
dangerous surf, the water temperatures remain above average (75
degrees) so decided to be prudent and add to the mix of coastal
hazards.
Expect a gradual recision of run up and high surf on Wednesday, so
these hazards will likely expire...but rip currents will remain
through at least sunset.
&&
.SHORT TERM...
(Tonight through Wednesday night)
Issued at 215 PM CST Tue Dec 3 2024
The latest radar and satellite imagery depicts overcast skies and
isolated to scattered showers across Deep South Texas and the Gulf
waters this afternoon. The highest coverage of showers remains
mainly along the immediate coast and Gulf waters, which coincides
with the highest precipitable water values and proximity to a weak
coastal low and associated frontal features. Surface observations
and the latest RAP analysis indicate the center of the coastal low
to be near or just south of the mouth of the Rio Grande River as of
this writing.
Unsettled weather will continue into tonight as the aforementioned
surface features translate north along the Lower Texas coast, with
the highest precipitation chances (40-70%) residing mainly along and
east of the I-69 corridor through midnight. Pockets of locally heavy
rainfall cannot be ruled out as moisture content remains high, but
the axis of rainfall should shift further north of the Lower Rio
Grande Valley over through the evening and tonight. After midnight,
we should begin to see activity begin to taper off from south to
north along the immediate coast as the coastal low translates north.
Precipitation chances are somewhat lower (30-40%) west of I-69
tonight, but light to moderate showers cannot be ruled out.
Otherwise, expect overcast skies and lows falling into the 50s
region wide, with the exception along the immediate coast with lows
in the low 60s.
Most precipitation chances on Wednesday and Wednesday night will be
confined over the Gulf waters and Lower Texas beaches, where the
slightly higher moisture content will reside. For the rest of Deep
South Texas, the combination of cloudy skies and generally light
winds will promote a pleasant day with highs mostly in the low to
mid 70s, slightly lower than seasonal normals for early December.
Winds will gradually shift to the south through Wednesday afternoon,
which will result in slightly warmer low temperatures Wednesday
night ranging from the upper 50s across the Rio Grande Plains to
upper 60s and low 70s across the Lower Rio Grande Valley and
immediate coast.
Along the Lower Texas beaches, a high risk of rip currents will
continue through Wendesday evening as winds and seas remain elevated
in response to the northward-moving coastal low.
&&
.LONG TERM...
(Thursday through next Tuesday)
Issued at 215 PM CST Tue Dec 3 2024
Upper level troughing over the western continental U.S. will bring
southwesterly flow aloft and coax a coastal low to meander north
early in the long term. As the coastal low pushes northward
Thursday, it will bring chances of rain, with highest chances
expected Thursday evening over the Gulf Waters before backing off
over the weekend. PoPs drop to less than 20% for the region, bar
along the coast, for the weekend and early next week. The fate of
next week lies in the timing and strength of a cold front
associated with the CONUS trough, which at this time are
uncertain, but continue to be monitored. European vs. North
American guidance both agree this trough will evolve into a cut-
off low over AZ/western Sonora by the weekend, however timing and
trajectory vary between each.
Temperatures start off near-seasonal in the beginning of the period,
with northern ranchlands highs near 70 and lows in the 50s, and lower
valley/coastal highs in the 70s - nearing 80 - and lows in the 60s.
Temps may creep up early next week as 850hpa winds advect the
shallow moisture remaining in the lower atmosphere. A tightening
pressure gradient ahead of the coastal low late Thursday/early
Friday will increase winds and return elevated seas, leading to a
likely chance of increased rip current risk for the local beaches
Friday.
&&
.AVIATION...
(00Z TAFS)
Issued at 654 PM CST Tue Dec 3 2024
Wind shift to the northwest behind the slowly departing coastal
trough has brought the relatively cooler air with it...as well as
IFR to LIFR ceilings for most. CAMs and NAM-12 are the better
models...but even they were tardy to the low ceiling party, so had
to fly by the observations to start the period. With just a slow
drop in temperatures and dewpoints expect ceilings to remain or
flirt between the IFR/LIFR line at Brownsville and Harlingen
overnight, with slightly higher levels at McAllen with a slightly
higher mixing layer below the stout inversion. Visibility is
dependent on rain...with a few more shower bands through mid
evening at Brownsville/Harlingen before they should taper down.
Still expecting some periods of 4-5 mile visibility overnight.
Ceiling will be slow to lift on Wednesday. Raised to low VFR at
McAllen for the afternoon, but held low MVFR during the same time
for Harlingen and Brownsville.
&&
.MARINE...
Issued at 654 PM CST Tue Dec 3 2024
Aforementioned rise in seas/swell to 10 feet and 9 second period
at buoy 42020 enough to both raise the values in the Coastal
Waters Forecast and the Small Craft Advisory hazard. Extended the
Advisory through noon Wednesday (seas) and may need to extend
longer for at least the 20-60 nm leg but perhaps all of the
waters, depending on swell direction by afternoon. A continued
east to east-southeast direction would push at least 7 foot waves
into the 10-20 nm portion of the nearshore, enough to extend all
Gulf waters through 6 PM.
&&
.MARINE...
Issued at 215 PM CST Tue Dec 3 2024
Tonight through Wednesday night...Adverse marine conditions will
prevail through late Wednesday night, with Small Craft Exercise
Caution to Small Craft Advisory conditions existing for the Laguna
Madre and Gulf waters. The Small Craft Advisory for the Gulf waters
will likely need to be extended for elevated seas through at least
Wednesday evening, although winds should begin to subside Wednesday
afternoon. Otherwise, expect scattered showers and isolated
thunderstorms through the period, which may result in locally
enhanced winds and seas.
Thursday through next Tuesday...Thursday evening through Friday
night, winds and seas may become elevated once again with potential
for Small Craft Exercise Caution conditions possible. Seas and winds
will diminish Saturday, leaving favorable light conditions. However,
a meandering coastal low will keep rain chances elevated in the
beginning of the period, with the greatest chance of rain Thursday
night at 70%. Moderate rain chances persist over the weekend,
primarily in the northern Gulf waters, before diminishing to early
next week.
&&
.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE 61 75 67 80 / 60 20 10 40
HARLINGEN 57 73 63 80 / 50 10 10 40
MCALLEN 57 73 64 80 / 30 0 10 30
RIO GRANDE CITY 52 72 60 75 / 30 0 0 30
SOUTH PADRE ISLAND 67 74 71 77 / 70 30 20 50
BAYVIEW/PORT ISABEL 60 74 65 78 / 60 20 20 50
&&
.BRO WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk through Wednesday afternoon for TXZ451-454-
455.
Coastal Flood Advisory until 5 AM CST Wednesday for TXZ451-454-
455.
High Surf Advisory until 7 AM CST Wednesday for TXZ451-454-455.
GM...Small Craft Advisory until noon CST Wednesday for GMZ150-155-170-
175.
&&
$$
SHORT TERM/MARINE/AVIATION Update...52-Goldsmith