Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/28/24
Area Forecast Discussion
National Weather Service Birmingham AL
828 PM CDT Fri Sep 27 2024
...New SHORT TERM...
.SHORT TERM...
(Tonight through Sunday)
Issued at 822 PM CDT FRI SEP 27 2024
Post-tropical cyclone Helene is currently centered near
Evansville, IN. Remnant tropical moisture is wrapping around the
back side of the circulation, but rainfall rates are light. Steady
light rain is located over our far northwest counties, while some
light rain bands are weakening in our northeast counties. Still
seeing some sporadic 30 to 35 mph gusts, so will keep the wind
advisory going, but it should be able to expire at 10 PM. Winds
will help keep temperatures up overnight. Wraparound moisture
lingers over the area tonight and tomorrow, with spokes of lift
rotating around the low causing light rain at times across the
north. Did expand low PoPs southward tomorrow afternoon where some
of the high res models indicate a band of light rain, but should
be low impact.
32/JDavis
Previous short-term discussion:
(This evening through Saturday)
Issued at 138 PM CDT FRI SEP 27 2024
This afternoon.
A highly amplified pattern was analyzed over the Country early
this afternoon with broad amplified ridging over much of the
Southern and Central Intermountain West while a deep-layer low was
over the Southern Tennessee Valley. Tropical Depression Helene
was located near the far eastern extent of Kentucky/Tennessee
State Line according to the latest NHC advisory. Multichannel
water vapor imagery along with the 27/12z BMX sounding depicts a
fairly dry airmass in the mid and upper levels over much of our
area, with more moisture in the low to mid levels per RAP 13 km
PWAT plots showing values near or just over 1.20 inches roughly
near and northwest of the Interstate 59 corridor.
Expect partly cloudy skies across the southern third of the area
with dry conditions today. More clouds with chances for isolated
showers are forecast for areas near and northwest of the
Interstate 59 corridor roughly. The best chances for showers will
be across our northwest 5 counties for this afternoon into the
evening as the tropical depression is forecast to decelerate as it
drifts west-northwest across South-Central Kentucky while the
upper low remains just to our northwest. Windy conditions will
continue to be experienced this afternoon with a wind advisory
remaining in effect for generally the northern half of Central
Alabama. Expect southwest winds from 15-25 mph with gusts
potentially up to 35 mph in higher elevations and in open exposure
locations. High temperatures will range from around 70 far
northwest to the low 80s across the southern quarter of the
forecast area.
Tonight.
Global modeling remains in solid agreement in the deep-layer low
absorbing/consolidating with the remnants of Helene overnight. The
upper low reflection is progged to move over eastern Tennessee
then loop northwest over Southwest Kentucky overnight, resulting
in a more vertically stacked system. At the surface, low pressure
will be centered across West-Central Kentucky overnight while a
surface trough will extend southwest from the low across the Mid-
South Region.
Expect partly cloudy skies with dry conditions across the
southern third of the forecast area overnight. Mostly cloudy to
cloudy skies will be found further to the north across our area
with lingering chances for isolated shower activity generally near
and northwest of the Interstate 59 corridor with scattered
showers forecast across our northwest 5 counties. Winds will
remain breezy as the pressure gradient slowly relaxes across the
region. Expect west to southwest winds from 10-20 mph on average
with decreasing speeds later into the night. Low temperatures will
range from the upper 50s across the northwest and north-central
quarter of the forecast area with low 60s expected elsewhere.
Saturday.
The deep-layer low will remain positioned over West-Central
Kentucky while the surface low becomes positioned slightly
northeast across North-Central Kentucky. A surface trough will
continue to extend southwest of the Surface low into the Mid and
Deep South Regions.
Partly cloudy skies are forecast areawide Saturday with mostly
cloudy skies across the northern third of the forecast area. Dry
conditions are expected across the southern third of the area
while isolated showers will be possible across the central third
of the area with scattered activity possible across the northern
third of the area. Winds will be breezy at from the west to
southwest from 10-20 mph at times. High temperatures will range
from around 70 far northwest to the mid 80s generally along and
south of the U.S. Highway 80 corridor.
05
&&
.LONG TERM...
(Saturday night through Thursday)
Issued at 244 PM CDT FRI SEP 272024
A large, closed low centered over Kentucky, will encompass most of
the eastern CONUS on Sunday. With our area on the southern side of
the low, a temperature gradient is expected from north to south,
in part due to cloud cover across our northern counties. As the
low wobbles around, mid-level vorticity may contribute to shower
activity along and north of I-20 Sunday afternoon. The low at 500
mb will begin to weaken on Monday as it shears into a weaker open
wave and gains forward speed to the east. Behind the departing
trough, we can expect dry and warm conditions for Monday through
Thursday.
87/Grantham
&&
.AVIATION...
(00Z TAFS)
Issued at 621 PM CDT FRI SEP 27 2024
Light rain, low clouds, and gusty winds continue to swirl around
Post-Tropical Cyclone Helene centered over Kentucky. One small
band of rain with brief visibility reductions is moving through
BHM/EET now. Will amend any other sites as necessary, but rain
should largely lift north of the terminals this evening.
Wraparound low-level moisture will cause cigs to lower to MVFR
and eventually IFR by Saturday morning at the northern terminals,
with a close call at MGM. Low clouds will linger on Saturday, but
should lift to VFR by mid-afternoon. Southwest winds will continue
to gust to 25 to 35 kts this evening, decreasing to 15 to 20 kt
gusts overnight and Saturday.
32/JDavis
&&
.FIRE WEATHER...
Southwest winds of 15-25 mph will continue this afternoon, and a
slow decrease in speed is expected for Saturday and again on
Sunday. Additional rain showers should be confined to our
northern counties, or along and north of I-20 through Sunday.
Minimum afternoon RH values through Sunday will range from 45
across the south to 70 percent across the north.
&&
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 63 73 60 80 / 50 30 20 20
Anniston 64 76 62 81 / 30 30 20 20
Birmingham 64 75 62 80 / 40 30 20 20
Tuscaloosa 64 78 62 83 / 30 20 10 20
Calera 65 77 63 82 / 30 20 20 10
Auburn 63 80 64 82 / 0 10 10 10
Montgomery 64 84 64 87 / 0 10 10 10
Troy 64 84 64 85 / 0 0 0 10
&&
.BMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 10 PM CDT this evening for the following
counties: Blount-Calhoun-Cherokee-Clay-Cleburne-Etowah-Fayette-
Jefferson-Lamar-Marion-Pickens-Randolph-Shelby-St. Clair-
Talladega-Tuscaloosa-Walker-Winston.
&&
$$
SHORT TERM...32/JDavis
LONG TERM....87
AVIATION...32
Area Forecast Discussion
National Weather Service Grand Rapids MI
1002 PM EDT Fri Sep 27 2024
.KEY MESSAGES...
- Showers Move in Saturday
- Lingering Chances for Light Rain Sunday-Tuesday
- Drying Out for Wednesday Through Friday
&&
.UPDATE...
Issued at 1002 PM EDT Fri Sep 27 2024
A few showers are developing in far southeast Michigan, moving
west. Latest guidance continues to suggest shower coverage
increasing and nudging northward into southern Michigan by early
morning, affecting mostly south of a South Haven to Lansing line.
HRRR forecast soundings for the Kalamazoo area during early
morning show some elevated parcels being weakly unstable up to
about -15 C, so a flash or two of lightning can`t be ruled out.
&&
.DISCUSSION...
Issued at 244 PM EDT Fri Sep 27 2024
- Showers Move in Saturday
Tropical Depression Helene is in the process of getting absorbed
into an upper low presently across KY/TN. The pressure gradient
force between this system and a high across the Upper Great Lakes
will lead to gusty winds on the order of 30-40 mph across the
region, especially in the 8pm-2am time frame tonight near and
south of M-46. The northern periphery of Helene`s rain bands will
likely make it as far north as southern Lower Michigan by
Saturday. GFS/ECMWF RH layers indicate saturating conditions in
the 925-700mb layer with PWAT values climbing to around 1.75",
quite high for late September. Rain showers will initially develop
in the early morning, moving from SE to NW, but as deep E/NE flow
takes hold, a more east to west banding is likely.
Model guidance is depicting narrowly forced rain bands, likely due
to the limited geographical breadth of deeper moisture overhead that
coincides with relatively weak frontogenetical forcing on the
northern periphery of a decaying Helene. All this to say that rain
amounts will be quite variable, with most areas less than 0.25" but
a few distinct, very narrow bands that could produce 0.50"-1.00" or
so, per the 12z HREF 24 hr LPMM through Saturday evening. The
northernmost extent of rain will likely halt somewhere near I-96,
so it is from that corridor to the south where the greatest
likelihood for showers will be. The highest amounts will likely
fall near and east of a AZO/LAN line. The Nam 3km and HRRR are
showing 100-300 J/kg of MUCAPE rooted above the 700mb layer where
a general lack of saturation is present, thus the threat for
thunderstorms is quite low.
- Lingering Chances for Light Rain Sunday-Tuesday
Low level moisture and precipitable water values around an
inch linger over the area into Tuesday. No one day will be a washout
but any slight amount of lift will result in drizzle or rain
showers. Monday`s chances are better in the afternoon as we see some
diurnal instability develop with mean CAPE values of 100 to 200
J/kg. Tuesday`s chances are better as the front moves through though
there is some uncertainty at the exact timing as seen in the
ensembles.
- Drying Out For Wednesday Through Friday
Behind the front Tuesday drier air filters in with northwest flow
becoming more geostrophic for the end of the work week. Temperatures
will be cooler as well with highs in the 60s and lows in the 40s.
With the cooler temperatures and partly cloudy to sunny skies,
weatherwise it will be a fitting start to October.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 722 PM EDT Fri Sep 27 2024
Moisture from Tropical Depression Helene will continue to try to
move into the region tonight. Ceilings will fall throughout the
night. The I-94 terminals have the best chance of seeing light
rain and IFR cigs after 06z. The I-96 terminals will likely remain
dry. Ceilings will gradually improve Saturday afternoon.
&&
.MARINE...
Issued at 244 PM EDT Fri Sep 27 2024
Winds over the nearshore waters are expected to gust into the
25-30 kt range across the SCA area near and south of Grand Haven,
lasting into at least Saturday morning. A possible extension may
be needed into Saturday afternoon depending on the persistence of
the higher winds. Given the ENE flow, the highest wave action will
be south of South Haven. Conditions do look to improve later
Saturday into Sunday.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 8 AM EDT Saturday for LMZ844>846.
&&
$$
UPDATE...CAS
DISCUSSION...Hoving/RAH
AVIATION...04
MARINE...Hoving