Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 170745
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
345 AM EDT Thu Aug 17 2017

.NEAR TERM...(Today through Tonight)
Issued at 339 AM EDT Thu Aug 17 2017

High impact weather potential: Scattered thunderstorms today into
this evening. Marginal risk of severe storms along and south of a
line from Manistee to Gaylord to Alpena with a slightly greater risk
along and south of M-55 from Houghton Lake to East Tawas. Main
threats are for damaging winds. A tornado is not out of the
question. Locally heavy rainfall.

Pattern synopsis and forecast:

Early this morning, a vigorous shortwave and associated sfc low
pressure was over srn MN, with a warm front extending ESE through
far srn Lake Michigan and nrn Indy. A band of showers, as well as a
pockets of thunderstorms in central/srn Lake Michigan, were lifting
NE as the srn MN low pressure system does the same. The BL moisture
was very moist per upstream soundings, and the LLJ/WAA coupled with
DPVA and upper divergence were the forcing mechanisms at play. Lapse
rates aloft leave much to be desired, not even hitting 6c/km.
Temperatures have remained warm overnight due to extensive clouds
sweeping in over the region, and strengthening southerly flow just
above the sfc. Readings were still in the 60s and low 70s.

The low pressure system will drive into the central upper peninsula
this afternoon, while dragging a warm front into nrn lower Michigan.
The band of showers and pockets of thunderstorms will lift into the
region through this morning, as height falls increase and steepen
the mid level lapse rates to a little over 6c/km, and while forcing
from the aforementioned mechanisms strengthen. The activity may fall
off to some degree behind this initial band of precipitation during
the late morning and early afternoon, but renewed showers and storms
are expected to fire along and ahead of the system cold front that
crosses the region through the evening hours. It is during the later
hours of the afternoon and early evening that the potential exists
for severe storms. This will significantly depend on whether or not
we can get some sort of sunshine and heating to develop enough
instability. If the middle 70s can be reached, we can generate up to
1200 j/kg of MLCAPE, as dew points will be in the middle and upper
60s. Lower 70s dew points are not out of the question nearer Saginaw
Bay. Bulk shear values will be 35-45 knots for potentially well
organized storms/supercells while the nrn fringe of the stronger mid
level jet core arrives (strongest winds in srn lower Michigan). Low
LCL heights of around 2200ft and potential back of the low level
flow and sfc-3km helicities at a very respectable 250 m2/s2 for the
potential for a tornado. Greatest threat for severe weather will be
between 4pm and 9pm, again for primarily along and south of M-55
from Houghton Lake to East Tawas, to a lesser extent, north of there
to Manistee to Gaylord and over to Alpena. Locally heavy rainfall is
certainly possible with the thunderstorms as PWATS will be very high
at around 1.85".

A break in the action is expected behind this cold front, before
deeper low level moisture sweeps into the region later in the night
for the potential for scattered light rains and/or drizzle. Lows
remaining mild tonight, in the lower to middle 60s.

&&

.SHORT TERM...(Friday through Saturday)
Issued at 339 AM EDT Thu Aug 17 2017

Friday...Low pressure will track from near the SOO to start the
period into east central Ontario by evening. There could be a few
wrap around lingering showers in the morning. In addition...shallow
over lake instability (925/lake delta ts between 6 and 7) will
likely help the cause off of Lakes Superior and Michigan under a
northwest flow producing scattered lake effect showers.
Meanwhile...low levels remain socked in with clouds for pretty much
the whole day. Cooler with highs only in the middle 60s to lower
70s.

Friday night...Perhaps a few evening lake driven showers in
northwest flow favored areas but lake instabilty then wanes
leaving mostly cloudy skies...except for partial clearing across
southwest zones late. Lows in the middle and upper 50s.

Saturday...A moisture starved short wave moves through the flow
(mainly to our south) bringing perhaps a few sprinkles...otherwise
partly sunny skies are expected. Warmer with highs in the middle to
upper 70s.

&&

.LONG TERM...(Saturday night through Wednesday)
Issued at 339 AM EDT Thu Aug 17 2017

Rising heights through Sunday then a northern stream short wave
knocks down heights while carving out a trough for the remainder of
the period. Warm temperatures Sunday and Monday will gradually cool
back off Tuesday and especially Wednesday. Threat for showers and
possible thunderstorms Monday afternoon (hope the eclipse doesn`t
get blocked) and am routing for the slower ECMWF for that reason.
There is a better chance for showers and storms Monday night into
Tuesday. Could even be a few lake effect driven showers Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday evening)
Issued at 1145 PM EDT Wed Aug 16 2017

Widespread showers and embedded thunderstorms will develop from SW
to NE late tonighT...Thursday and Thursday night as low pressure
tracks NE out of the Central Plains and into the Western Great
Lakes region. Conditions will deteriorate to widespread MVFR as a
result...with a few locations experiencing IFR conditions at
times. SE winds AOB 10 kts overnight will become S/SE and
strengthen to 10 to 20 kts with some higher gusts expected.


&&

.MARINE...
Issued at 339 AM EDT Thu Aug 17 2017

Strong low pressure will cross through eastern Lake Superior
tonight and into western Quebec by Saturday morning. Strengthening
winds out of the SE will swing more SW later this afternoon and
tonight behind a cold front, then more NW Friday into Friday
night. The pressure gradient will be tight enough for period of
advisory level winds over this time. Have expanded the advisories
to include all nearshore waters through today and several more
into Friday.

Periods of showers and thunderstorms can be expected today into
tonight, with the stronger storms expected over the Lake Huron
waters. There is potential for severe storms. More scattered light
rain and drizzle expected for Friday.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY from 8 AM this morning to midnight EDT
     tonight for LHZ346-348-349.
     SMALL CRAFT ADVISORY from 8 AM this morning to 8 PM EDT this
     evening for LHZ345-347.
LM...SMALL CRAFT ADVISORY from 8 AM this morning to noon EDT Friday
     for LMZ323-342-344>346.
     SMALL CRAFT ADVISORY from 8 AM this morning to 8 PM EDT this
     evening for LMZ341.
LS...SMALL CRAFT ADVISORY from 8 AM this morning to midnight EDT
     tonight for LSZ321-322.
&&

$$

NEAR TERM...SMD
SHORT TERM...AS
LONG TERM...AS
AVIATION...MR
MARINE...SMD


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