Area Forecast Discussion
Issued by NWS Gaylord, MI

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893
FXUS63 KAPX 170345
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1145 PM EDT Wed Aug 16 2017

.UPDATE...
Issued at 1001 PM EDT Wed Aug 16 2017

Low pressure continues to develop along the Iowa/Minnesota
border...and is slowly tracking eastward into the Western Great
Lakes area. Leading edge of cloud cover associated with this
system has reached our SW CWA...with the leading edge of
associated precip now extending from OSH to near MKG. Latest near
term models still hold off until after 06z for any significant
increase in POPs from SW to NE across our CWA. This seems
reasonable given projected timing of upstream precip into our
area.

&&

.NEAR TERM...(Tonight through Thursday)
Issued at 308 PM EDT Wed Aug 16 2017

...Rain Thursday...

High impact weather potential...Thunderstorm (severe?) and heavy
rain potential Thursday.

Upper ridge over region with 1020mb surface high centered over
southern Ontario. Upper trough in the Plains with surface low in
Iowa. Ridge axis moves across Michigan this afternoon.

Trough and surface low translate east overnight. Low deepens as it
moves as it moves into northern Wisconsin tomorrow afternoon and
into the UP by evening. Potential for thunderstorms and heavy rain
with this system. Best potential will be near the surface low in the
eastern UP (best forcing) and also across areas south of CAD to APN
(best instability). Warm front with the low enters the KMBL
area around 12Z reaching the Straits/UP by 00z.

Precipitation will come in two waves. First deep moisture and
isentropic ascent arrives along/ahead of the warm front with help of
30-40kt low level jet around daybreak. BUFKIT shows very skinny
elevated CAPE with values to 500 J/kg near warm front with
30-40kts of 0-6km Bulk Shear, so thunder possible. This will trend
the start time sooner than previously thought. Also means clouds
moving in faster which will cut down on any sunshine and daytime
heating expected.

Later, narrow warm sector arrives with dewpoints near 70F, PWATs
approaching 2 inches and CAPE values close to 2000 J/kg ahead of the
cold front. Lapse rates are marginal and lack of daytime heating but
mid level speed max and left exit region of upper jet should
enhance lift. 0-6km Bulk Shear values increase to 40+kts near
Saginaw Bay. So definite chance of thunder, especially near the
cold front. Enough shear that isolated severe not out of the
question, especially south. If there is enough instability to get
organized convection, could see quite a few severe thunderstorms,
especially south of M-55. Updated SPC day 2 outlook now includes
slight risk of severe thunderstorms near Saginaw Bay, surrounded
by marginal that includes areas south of MBL-APN. Big question is
how far north the warm sector gets.

In any case, plenty of moisture and lift for all areas to receive
descent amount of rainfall Thursday and enough instability for some
thunderstorms. Southern areas should see the best chance for
convection. Pretty much a washout for outdoor activities Thursday.

&&

.SHORT TERM...(Thursday night through Saturday)
Issued at 308 PM EDT Wed Aug 16 2017

...Friday looks a touch ugly but Saturday should be better...

High impact weather potential...t-storms with potential heavy rain
linger into Thu Night.

Low pressure will deepen as lifts across upper MI and Lk Superior
Thu night and early Friday. Associated cold front will cross the
region Thu night. Deep moist convection will continue Thu night
ahead of the front, though surface fropa will be gradually cutting
that threat off as the night proceeds. Friday will be a classically
grungy post-frontal day, with cool/moist air supporting (and the
lakes enhancing) showers/drizzle. We`ll shake loose of that pattern
by Saturday, as the low ejects into northern Quebec.

Pops remain high for Thu evening, especially in eastern and northern
portions of the forecast area. Near-term fcst thoughts re: heavy
rain and svr threat still apply for a portion of the evening.
Wraparound moisture will spill back into eastern upper/nw lower MI
overnight. That will gradually depart Friday, though as 850mb temps
fall back to 8-9C, warm Lake Mi will compensate to some extent.
Highest pops overnight/Fri morning in eastern upper/nw lower MI,
with pops dwindling for the rest of the day, and ending toward
midnight.

Min temps Thu night will be mild, as the main push of cool air
arrives Fri morning. Lows will be mainly in the low/mid 60s.
However, max temps Friday won`t get very far. Highs upper 60s to
lower 70s.

Clouds will tend to diminish Fri night and especially Saturday, as
the 850mb thermal trof get displaced and warm advection arrives on
backing 1000-850mb winds. A shortwave will be skirting the southern
lakes on Saturday, especially early. Most of the associated precip
will be to the south. However, influence of the system when combined
with diurnal heating might have an outside shot at busting out a
shower near Saginaw Bay. Otherwise dry, with again a tendency for
decreasing cloudiness.

Min temps Fri night in the 50s. Max temps Sat in the 70s.

.LONG TERM...(Saturday night through Wednesday)
Issued at 308 PM EDT Wed Aug 16 2017

Height falls working into the region early in the week will bring
the best chance of widespread showers over the extended. Timing
right now looks to favor Tuesday. Can`t completely rule out some
isolated showers Monday with a weak boundary passing through and
good return flow starting to increase moisture as high pressure
slides through the Ohio Valley Sunday. Blends right now are trending
towards at least partly cloudy skies for Monday, which at this time
seems reasonable. Will have to see how strong and how long the
moisture advection affects the area prior to Monday. Temperatures
expected to run a bit above normal heading into midweek.

&&

.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 308 PM EDT Wed Aug 16 2017

Small Craft Advisories may be needed Thursday and Friday.
East to southeast winds ahead of our next storm system will
continue through Thursday. Winds will increase to near Small Craft
levels after daybreak Thursday on all the big lakes. Gusty marine
winds are expected to continue into Friday.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY from 8 AM to 8 PM EDT Thursday for
     LHZ345>349.
LM...NONE.
LS...SMALL CRAFT ADVISORY from 8 AM to 8 PM EDT Thursday for LSZ321-
     322.
&&

$$

UPDATE...MR
NEAR TERM...KF
SHORT TERM...JZ
LONG TERM...AM
AVIATION...MR
MARINE...KF



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