Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 231405
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1005 AM EDT Sun Jul 23 2017

.UPDATE...
Issued at 1005 AM EDT Sun Jul 23 2017

Surface low has reached the Straits area...with the upper level
low close behind over Western Upper Michigan. Deep cyclonic flow
and strong upper level divergence just ahead of the upper low
continues to generate several areas of convection over Upper
Michigan. Overall intensity is rather weak due to lack of
instability...but this convection is certainly producing some
pockets of heavy rainfall of half to one inch per hour per latest
KAPX precip estimates across Chippewa and Mackinac counties.
Expect this precip will expand southward into Northern Lower
Michigan as we head into the afternoon and evening hours as the
upper low swings into the region during peak heating/instability.
And that is the real question...will we be able to destabilize
enough to produce some stronger/possibly severe storms this
afternoon/early evening. Latest vsbl satellite shows quite a bit
of cloud cover across our CWA...which appears to be expanding over
time. Certainly think a few stronger to borderline severe storms
are not out of the question during peak diurnal instability as the
upper level feature swings thru. 0-3 km bulk shear values are
around 30 kts and projected MUCAPES reach near 2000 J/kg in our SE
CWA per the latest NAM. Suspect this value could be lower if low
clouds continue to expand.

&&

.NEAR TERM...(Today through Tonight)
Issued at 327 AM EDT Sun Jul 23 2017

...Thunderstorm chances today...possible severe...

High Impact Weather Potential...Marginal chance of severe storms
with a slight risk along and south of M-55.

Pattern Synopsis/Forecast...Overnight satellite/upper air/surface
analysis reveals suppressed heights and a baroclinic zone across
the Great Lakes through New England with a pronounced short wave
advancing southeastward through western upper Michigan.
Substantial heat/instability is suppressed from the Ohio Valley
southward...but there is a tongue of instability that stretches up
into the western Great Lakes through Wisconsin...ahead of
developing surface low associated with the incoming wave. Several
pockets of showers/storms are underway ahead and underneath the
short wave...most notably one line of showers/sub-severe storms
crossing the southwestern part of CWA early this morning and
additional showers/storms in parts of eastern Lake Superior.

Mid level short wave and primary QG-forcing for ascent will cross
northern Michigan through the course of the day and into the
eastern lakes region tonight. Attending elongated surface low and
tongue of instability slides southeastward across lower Michigan
through the course of the day...providing some additional low
level convergence for ascent.

Primary Forecast Concerns...Severe storm possibilities today.

Forecast PoP timing/coverage remains a bit nebulous with this
system but will likely be largely tied to the daytime heating
cycle along with help from inland terrain and low level
convergence axis that follows the surface low. May also see some
earlier showers/storms expand out of eastern Lake Superior into
eastern upper Michigan and parts of northern lower Michigan this
morning owing to increasing QG-forcing for ascent ahead of the
short wave. In any event...will keep with the idea of highest pops
this afternoon/early evening during peak heating and with arrival
of slightly cooler air aloft...and again across eastern upper and
northeast lower Michigan aided by terrain and inland convergence.

Severe weather possibilities...better instability will be had
across northern lower Michigan and particularly across the SE part
of the CWA where forecast soundings suggest MLCAPE values in
excess of 1500 J/KG during peak heating...along with modest 0-6 KM
bulk shear values in excess of 30 knots. Enough for a slight risk
for severe provided we get the needed heating.

&&

.SHORT TERM...(Monday through Tuesday)
Issued at 327 AM EDT Sun Jul 23 2017

...High pressure...

High Impact Weather Potential...none

Pattern Synopsis/Forecast...High pressure builds into the region
and squashes all convection through the 48 hour period. This
should produce mostly sunny skies through the period as well as
temperatures recovering from below normal (Sunday and Monday) to
normal (Tuesday). This could cause some issues fire weather-wise
as the relative humidity looks to fall to around 40% on the models
for Tuesday afternoon. The only time there could be some
precipitation would be between 09z and 12z/Wed (Tuesday night).
Rain showers may get into E Upper as the cold front moves into the
Upper Great Lakes.

Primary Forecast concerns...With high pressure, you`d think that
there`d be any concerns, but... The problem would be with the dry
air aloft, there is a possibility that if we can mix deep enough,
we could end up below 30% relative humidity on Tuesday afternoon.
At this point, the probability would be about 10%, so will
continue to evaluate it from day to day, but not something to
discount.

.LONG TERM...(Tuesday night through Saturday)
Issued at 327 AM EDT Sun Jul 23 2017

...High pressure looks to dominate the next week...

High Impact Weather Potential...Thunderstorms Wednesday. Elevated
fire weather conditions possible for Friday and Saturday, but that
is probably a low chance probability.

Extended (Wednesday through Saturday)...The majority of the last
half of the week will be dominated by high pressure and temperatures
around normal. There are only a few things that we will have to
worry about in the days to come. Wednesday, a cold front moves into
the forecast area and moves across it through the day. This will
kick off showers and thunderstorms as it moves across the region. It
does look like we will have instability, lift and shear, so we will
have to keep an eye on that as well. The other thing to watch is
that as we head into the weekend, Friday and Saturday have the
potential to be dry enough that we could have elevated fire danger.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 535 AM EDT Sun Jul 23 2017

MVFR-pockets of IFR CIGS have been slowly devleoping across
northern lower Michigan over the last several hours...and will
hang around for a good part of the day particularly across
northeast lower Michigan and the tip of the mitt. Showers and a
few thunderstorms will also expand across the region
today...especially this afternoon with daytime heating. PLN/APN
have the best chances for those showers/storms.

CIGS/VSBYS lower tonight into the MVFR-IFR category as cooler air
sags into the region.

&&

.MARINE...
Issued at 327 AM EDT Sun Jul 23 2017

Sustained winds remain largely 15 knots or less through Monday
with waves under 4 feet. Thus no marine headlines anticipated.
Stronger winds/higher waves likely to impact parts of Lake Huron
later today through Monday morning with winds becoming
northeasterly.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY from midnight tonight to 11 AM EDT Monday
     for LHZ348-349.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...MR
NEAR TERM...BA
SHORT TERM...JL
LONG TERM...JL
AVIATION...BA
MARINE...BA



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