Area forecast discussion
National Weather Service Marquette Michigan
1209 am EDT Thursday Jun 20 2013
Short term...(this evening through thursday)
issued at 429 PM EDT Wednesday Jun 19 2013
WV imagery and RUC analysis indicated west-northwest middle/upper level flow
through then northern Great Lakes between a trough over eastern Canada and a
ridge over the plains. Scattered rain showers and isolated thunderstorms and rain had developed near
cyrl on the tail of a shortwave trough through northwest Ontario. An
upstream shortwave was also located over eastern South Dakota. At the surface...srly
winds had increased between high pressure over the eastern Great Lakes and a
trough extending into ND from low pressure west of James Bay. Low level
moisture was only slowly increasing with dewpoints climbing to near
50f over the west.
Tonight...even though the forcing with the northwest Ontario shortwave will
remain north of the County Warning Area...models suggest that the rain showers and possibly
some thunderstorms and rain will develop later this evening northwest of Lake Superior and
slide into the western County Warning Area overnight. Moisture transport and the
position of the 850-700 mb frontal zone favors greater precipitation
chances/coverage over Northwest Lake Superior into mainly the northwest County Warning Area.
MUCAPE values are expected to be high enough for elevated thunderstorms and rain
development.
Thursday...the combination of increasing moisture
transport...daytime heating and the South Dakota shortwave should bring
increasing rain showers/thunderstorms and rain coverage across the County Warning Area. Although instability
will be marginal for stronger storms with MLCAPE values into the
500-1000 j/kg range...and a relatively Narrow Cape profile....some
storms with small hail and gusty winds to 35 miles per hour may be possible.
Long term...(thursday night through wednesday)
issued at 429 PM EDT Wednesday Jun 19 2013
Convection will make for a very tricky and uncertain forecast Thursday
night through at least the weekend.
An upper ridge will move east into the area Thursday night through the
middle of next week. At the surface...a weak low will remain fairly
stationary over the central and northern plains...leaving a warm front
across or near the County Warning Area through this weekend. Confidence is very low
/as with most convective situations/ with the exact track/timing of
any convective complexes moving along or near the warm front. Models
show multiple scenarios for convective development and
movement...including moving the warm front north of the County Warning Area keeping the
bulk of convection north of the County Warning Area...to having the warm front stall S
of the County Warning Area which would keep most of the convection S. Overall...the
bulk of the models show convective complexes moving over the
County Warning Area...so will continue to put that into the forecast as has been
done by previous shifts.
Some of the thunderstorms could very well be strong with large hail
and damaging winds the primary threats...but confidence is still too
low to incorporate that into the forecast but will continue some
mention of stronger storms in the severe weather potential statement. Storm Prediction Center has areas along the
border under a slight right...and generally agree with that given
the location of the greatest instability. Models show up to 4500j/kg
/GFS/ of SBCAPE nosing into western Upper Michigan Friday afternoon...but that is
the highest amount and looks like low levels are overly moist in the
model. The NAM is another model that seems too high on low level
moisture and SBCAPE at up to 3500j/kg on Friday. European model (ecmwf) and Gem seem
more reasonable at 1000-1500j/kg along the WI border so will favor
that solution. Could have daytime convection break out over western and
central Upper Michigan...but most likely scenario at this point continues
to be convection forming upstream and moving to the east-southeast along the
forward propagating corfidi vectors and instability gradient Friday.
Another risk factor will be heavy rain with any thunderstorms as
precipitable waters will be 150-200 percent of normal.
Sat and sun look similar to Friday...with similar uncertainty due to
convective uncertainty. In fact...similar conditions should be
observed into the middle of next week...but confidence increases too
much Monday-Wednesday to talk too much about this time frame.
Looking at temperatures...should see surface temperatures increase slightly from day
to day through the forecast peroid with highs in the 80s across a
large part of Upper Michigan by sun.
&&
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1209 am EDT Thursday Jun 20 2013
Overnight...attention turns to surface trough dropping S toward the upper
lakes in association with shortwave currently passing through northern
Ontario. Scattered rain showers and diminishing thunderstorms and rain have been occurring
along/ahead of trough...and some of those rain showers will hold together and
affect kcmx overnight and then possibly kiwd/ksaw this morning.
Confidence in rain showers occurring at kiwd/ksaw is lower than at kcmx...so
only vcsh was utilized at those 2 terminals. Despite -shra...initial
drier air at the low-levels should result in VFR conditions into the
morning. However...will need to watch kcmx as any upslope wind off
the lake could result in lower clouds/fog possibly forming this
morning. This afternoon...daytime heating should generate scattered rain showers/thunderstorms and rain
across Upper Michigan with better potential at kiwd/ksaw. There is limited
confidence in precipitation actually occurring at a terminal...so only thunderstorms in the vicinity
was included in forecast. If rain showers/thunderstorms and rain occur at kiwd/ksaw...MVFR
conditions would likely accompany precipitation. Scattered convection should end by
evening. During the evening...combination of a cool easterly upslope
wind off the lake into higher dewpoint air over the Keweenaw may result
in fog/stratus developing at kcmx.
&&
Marine...(for the 4 PM Lake Superior forecast issuance)
issued at 429 PM EDT Wednesday Jun 19 2013
Winds should remain below 25kts through the period...with relatively
low waves. The main hazard will be stronger winds/hail/lightning
with any thunderstorms moving across Lake Superior from late tonight
through into early next week. Areas of fog that develop as a result
of increased moisture and shower activity may also become locally dense.
&&
MQT watches/warnings/advisories...
Upper Michigan...
none.
Lake Superior...
none.
Lake Michigan...
none.
&&
$$
Short term...jlb
long term...Titus
aviation...rolfson
marine...jlb
