Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/29/16
Area Forecast Discussion
National Weather Service Birmingham AL
555 PM CST Wed Dec 28 2016
For 00Z Aviation.
In the short term, we`ve added some POPs to the southern counties
through the rest of this afternoon based on radar trends. The big
action remains to our northwest right now, with left-moving hail
producing cells in western TN. Those particular cells should stay
to our north.
Later on tonight, however, additional showers and storms are
expected to develop and move into our area. Will maintain the
status quo on severe threat graphics and products. HRRR output
lends some support to the idea from this morning`s discussion that
cellular activity, oriented in a SW-NE band, and moving toward
the ESE, could bring some gusty winds or isolated tornadoes into
central Alabama. It is still very low confidence, but non-zero
enough to maintain a close watch. Using HRRR timing suggests first
cells could reach our NW counties as early as 10 pm, and exit the
SE by 10 am Thursday.
In the longer term, I`ve added a brief mention of sleet with the
onset of precipitation on Saturday. We often get some "warm sleet"
in top-down moistening situations such as this, as the rain aloft
falls into a drier low level layer. Eventually, the low levels get
overwhelmed with warm enough and moist enough air so that
everything becomes rain, so the window of opportunity is just a
few hours at most. I also adjusted POPs a bit in the Saturday
through Sunday time frame -- mainly making them higher, as
confidence in a rainy situation increases.
No other changes were made in the forecast beyond that point.
00Z TAF Discussion.
No large changes to the forecast this TAF cycle. I did push back
the timing of the thunderstorms at each location. I really don`t
think the rain and storms will last more than a couple/few hours
at any location. Before the main line/band of storms arrive,
ceilings will be all over the place. Initially, at worst, expect
MVFR conditions. There could be some IFR eventually, either before
during the time rain moves in, but I think that would be the
exception rather than the rule. Conditions should improve quite
rapidly after the rain exits, as winds pick up and become quite
gusty out of the northwest.
A cold front will move through tonight, bringing a line of
showers and a few thunderstorms. A drier air mass will move in
behind the front on Thursday through the end of the week. RH
values will fall into the 30s Thursday and Friday with breezy
conditions, but critical fire weather thresholds are not expected
to be met. A wetter pattern will return for the weekend.
Area Forecast Discussion
National Weather Service Columbia SC
1030 PM EST Wed Dec 28 2016
A cold front stalled just south of the area may return northward
as a warm front tonight ahead of a stronger cold front that will
cross the area Thursday. Canadian high pressure will build across
the region Friday and Saturday. Increasing moisture from the Gulf
of Mexico will bring the chance for wet weather during the
beginning of the new year.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Low temperatures overnight will be dependent on the amount of
clearing that can occur from the higher clouds through about 05z
or so before the warm advection increases ahead of the next front
and low clouds return. Think lows will occur in the 04z-08z time
frame with temperatures holding steady or increasing late tonight
as strong southerly 45-50 knot 850mb flow moves over the area and
mixes the boundary layer and dewpoints rise with strong moisture
transport. Expect lows ranging from the lower 40s northern
Midlands to upper 50s CSRA.
Rain chances will increase after 06z with isentropic lift
strengthening and atmospheric moisture increasing rapidly ahead of
the approaching cold front. Latest SPC HRRR slows timing of
precipitation somewhat and weakens the overall line of showers
through daybreak Thursday, so have made some minor adjustments by
lowering pops a bit and slowed timing by a couple of hours. Surface
instability is not overly impressive but will keep mention of
slight chance thunder mainly in the 10z-14z time frame. Do not
expect any severe weather.
.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
A cold front will push through the forecast area Thursday morning.
Low level convergence ahead of the front and moisture advection in
SW 850 mb flow suggests showers are likely. Showers will move
quickly through the region as mid-level winds become westerly
after 12Z. The main area of showers should be east of the
forecast area after 15Z. There will be a chance for thunderstorms
Thursday morning as models indicate some elevated, potential
instability. Severe weather potential will be minimal given stable
High temperatures will be in the mid to upper 60s given
downsloping low level flow from the west northwest and clearing
skies. But temperatures will begin to fall later in the afternoon
as cooler air, delayed by the Appalachians, moves into the area.
Sustained winds from 15 to 20 kts with gusts up to 30 kts will be
possible behind the front Thursday afternoon. NW Winds will stay
up Thursday night and continue through mid-day Friday. The
pressure gradient begins to weaken Friday afternoon. A Lake Wind
Advisory may be needed through Friday for sustained winds around
20 knots over the lakes.
Friday will be clear but much cooler with high temps in the upper
40s north to lower 50s south as the surface high drops to the
northern gulf coast, keeping the area in the cold advection
regime. Near ideal radiational cooling Friday night under clear
skies and light winds will allow temperatures to fall into the 25
to 30 degree range.
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
In the long term, an upper level trough will move into the south
central CONUS. Temperatures will gradually increase as Gulf
moisture moves into the region and cloud cover increases. Models
continue to differ in the timing and location of frontal
boundaries but Monday and Monday night appear to be the best
chance of seeing precipitation. With moisture advection persisting
through much of the long term, cannot rule out at least a slight
chance of showers through the period. Temperatures become above
normal by mid-week.
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Only change to this aviation update was to add llws later on
tonight ahead of the front.
VFR conditions will remain through at least 06z, then expect the
beginning of restrictions with ceilings falling to MVFR/IFR by
07z-09z. An approaching cold front will remain west of the cwa
through 12z. Moisture advection ahead of the front may bring a few
showers into the area late tonight and early Thursday morning.
Have begun vcsh at most sites between 10z and 11z, then going more
predominant rainfall just ahead of the front between 12z-15z. Main
front should be pushing through the cwa between 13z-17z.
Light and variable winds early tonight, then increasing more out
of the south after 08z as pressure gradient increases. Model time
sections indicate a strong low-level jet of 40 knots around 2kft
developing later tonight. Have added llws to all tafs from approx 10z-
14z, then mixing should bring stronger winds and gusts down to
surface. Winds will shift more out of the west as the front
passes through, with wind speeds increasing behind the front to 15
to 20 knots with gusts to 25 knots. This will last through the end
of the 24 hr taf period. Ceilings should be improving behind the
front as much cooler and drier air builds into the region.
EXTENDED AVIATION OUTLOOK...Conditions will improve to vfr Thursday
night as drier air moves in, and mostly clear skies are expected
into the weekend.
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
738 PM EST Wed Dec 28 2016
00Z DTX sounding still revealed a substantial amount of dry air
in the low and mid levels. Radar and surface obs indicating virga
associated with the cold front showing up along a southwest to
northeast line from South Haven to Tri-Cities region. The issue is
we are running out of time and real estate for the moisture over
Central Indiana/Northwest Ohio to sneak across the border. The 22Z
HRRR clips far eastern areas (Monroe-Detroit-Port Huron) with some
light snow, but just a glancing blow. Minor update to trim back
pops everywhere and lower snow amounts slightly. Any snow activity
around should be over at or shortly after 3 AM.
Issued at 609 PM EST Wed Dec 28 2016
Main Adjustment of the tafs was to bump up the start and end time
of the snow, as well as shorten up peak time. Regardless if
northern terminals get snow, MVFR ceilings expected to develop
toward midnight as cold front pushes through. There is a low
chance the dry slot overnight into tomorrow morning could allow
for SCT clouds, best chance DTW-YIP-DET, but otherwise MVFR
ceilings expected to hold through the day as strong westerly winds
sustained at 15 knots gusting to 25 knots transport some
flurries/light snow showers from Lake Michigan during the
For DTW...Quick burst of snow expected just before Midnight, leading
to about half an inch of accumulation or slightly better before
ending around 7z. Brief mix of rain to start but not included in
TAF. It`s possible for some breaks in the MVFR clouds to develop
overnight into tomorrow morning before better cold advection kicks
in during Thursday. Westerly winds expected to gust to at least 25
knots at times with good low level mixing. Good chance for at
least some light snow showers to make it in late in the day, and
could persist during the evening hours.
//DTW Threshold Probabilities...
* High for ceiling below 5000 ft mid evening through Thursday
* Low for 1/2sm visibility in moderate snow around Midnight.
* Medium for a brief mix of rain and snow pellets at onset then
becoming all snow. High confidence in snow showers as precip
type Thursday afternoon.
Issued at 315 PM EST Wed Dec 28 2016
Energetic upper level flow with digging trough over the Central
Conus advancing east. Aggressive 6 hr 500 MB height falls sliding
through the Great Lakes/Ohio Valley Tonight, with max center progged
to track through Northwest Ohio. This also looks to be where the top
of the better moisture plume coming out of southern
Missouri/Arkansas will reach this evening, as seen in the 850-700 MB
Theta-E fields, as low level flow does not back all that much. Even
though northwest Ohio appears to be in best spot in terms of
moisture, lowering static stability, and forcing (700 mb FGEN
placement), there does appear to be just enough moisture sneaking
past the Michigan border, as 850-700 MB specific humidity reaches
around 3 G/kg into Detroit Metro Area by Midnight. With support from
12z NAM/GFS/GEM and majority of GFS ensemble members indicating qpf
of a tenth of better across the far east, will go along with the
streaking/expanding northeast snow shield East of U.S 23 late this
evening (3-7z) with the good left exit jet forcing. Window for snow
will be short, and with marginally cold surface temps in place,
thinking half an inch to around 1 inch is pretty good east of U.S
23, little to none west of U.S. 23, with perhaps up two inches as
once gets toward the Downriver area of Detroit to Port Huron.
However, it should be noted 17z RAP/HRRR indicating the
precipitation shield missing us just to our southeast, which lowers
confidence of the forecast. The 12z Euro is also less than
aggressive and adds to the concern of a miss.
Assuming we get the precipitation, with surface temps above freezing
to start, brief sleet/rain mix to start not out of the question
(modest 2-3 kft warm layer per nam sounding) before wet bulb/dynamic
cooling takes place with higher rates. Mid level dry slot and sharp
low level wind shift to the west by 9Z, ending snow by Morning rush
hour. However, cold advection (850 mb temps falling to -10 to -11 C)
over Lake Michigan, coupled with the good cyclonic flow extending
above 700 MB, good shot at light snow showers developing during the
day, continuing into Thursday Night, as cold advection continues,
with 850 MB temps falling into the negative mid teens. Decent
signals in NAM/GFS with a surface trough/I-94 type band developing
Thursday Evening/Night, and would expect some light accumulations
Heights begin to build on Friday as shortwave ridge advances toward
the Central Great Lakes, with the general subsident regime and
lowering inversion heights ending Lake effect activity, but may
take until late in the day, as 12z euro maintains cold 850 mb
temps of -13 to -15 C for much of the day.
By the start of the weekend and the last day of the year, a surface
low will be sliding across the northern Great Lakes bringing chances
for rain/snow to Southeast Michigan. This low looks to quickly push
east of the area as high pressure slides in behind bringing drier
conditions for the start of the New Year. More unsettled weather
then follows for the first part of next week as a potential system
moves up from the southwest. Temperatures will continue to remain at
or above normal for the extended forecast period.
South wind will continue to increase over Lake Huron tonight ahead
of a cold front moving through the western Great Lakes. The flow is
warmer and will force a shallower mixed layer over the water with
time. The increased stability will limit wind gusts to around 30
knots over the open waters. There could be a gust near gale force
briefly across the central portions near the international border
but the marginal speed and short duration does not support a
headline. The passage of the cold front will turn the wind westerly
Thursday morning and then northwesterly during the afternoon. Speed
is expected to reach gale force with bands of snow squalls by
Thursday night as deep instability develops over the lake. The gales
are likely as low pressure near Georgian Bay merges with a powerful
system developing over the New England states. A gale watch is in
effect for the central and north portions of Lake Huron through
Friday morning. High pressure Friday afternoon is projected to move
quickly through the region and the next low pressure system is shown
to be weaker Friday night into Saturday.
Lake Huron...Gale Watch from Thursday evening through Friday morning FOR
Small Craft Advisory until 3 AM EST Thursday FOR LHZ441-442.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Tulsa OK
827 PM CST Wed Dec 28 2016
Current forecast on track for tonight with just minor changes for
sky cover and temps. Front has moved through the CWA and
continues to push southward through northern Texas. A pocket of
moderate fog has developed over portions of west-central Arkansas
and southeast Oklahoma this evening. The HRRR has a good handle on
this and quickly dissipates the fog as the front slides south and
lower dewpoints move in behind the front.