Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
342 am EDT Tuesday may 21 2013
Short term...today and tonight
Line of thunderstorms currently over northern Illinois is slowly but
surely marching northeast during the early morning hours. The main
question this morning is how well this activity will hold together
as it tracks through Southeast Michigan. Hi-res model runs are in
general agreement in bringing the system through between 09-13z.
That is where the agreement ends as the hrrr lifts the best
thunderstorm activity north through northern lower Michigan while
the WRF maintains the line of strong thunderstorms as it tracks
through Southeast Michigan...mainly north of the M-59 corridor. The
evolution of the jet stream would validate the hrrr solution as it
lifts the 100+ knot jet north over the northern Great Lakes...taking
the upper level divergence afforded by the right entrance region of
the jet with it. However lower levels lend credence to the WRF
solution as the main shortwave driving the northern edge of the
convection is prognosticated to go directly through Southeast Michigan with
the nose of the 35 knot 850 mb low level jet pointed over Southeast
Michigan. Despite the loss of upper level jet support...the lower
level dynamics point to an active morning across Southeast Michigan
with the line of convection expected to survive the trip and track
through the area. This activity will still have quite a bit of
instability to work with as MUCAPE values remain at 1000 to 1500
j/kg during the early morning hours. Severe weather threat from this
mornings convection will mainly be a wind threat...as upstream
observations show little threat from large hail...although small to
near severe hail is a possibility.
After this initial activity the picture becomes very muddled as the
nwp models keep showers and thunderstorms going for much of the day.
This scenario is certainly plausible as another jet streak lifts
from the southwest and makes its way over the Great Lakes region. As
a result the area will be in the path of several shortwaves rotating
around the main middle level low pressure system taking up residence
over the Missouri Valley. Without a key feature indicating there
will be a substantial break from the action...do not plan on
deviating much from the previous forecast high probability of precipitation through the
daytime hours.
Severe weather potential this afternoon will hinge on the ability to
get a break in the convection. This window will not have to be
large...as evidenced yesterday...with a brief break allowing
temperatures and convective available potential energy to rise significantly in a short period of
time. Models show MUCAPE values ranging from 500 to 1000 j/kg with a
fairly steady stream of convection during the day. Afternoon
sunshine could easily boost these values to around 1500 j/kg given
the late may sun angle and the very warm air in the low levels. In
addition to the instability...0-6 km bulk shear values are a good 30
to 40 knots today...meaning the potential for strong to severe
thunderstorms producing damaging winds and large hail are a
possibility. Closer inspection of the hodograph and low level cape
show isolated tornadoes will also be a threat...especially if we can
get some sunshine...as 0-3km cape values reach 150 to 200 j/kg and
storm relative helicity values get to 150 to 200 m2/s2. All of this
activity makes forecasting high temperatures today quite
challenging. Even with all of the activity we should be able to get
into the low 80s away from the Great Lakes...however a few middle 80s
are a distinct possibility if the aforementioned break in the
activity occurs.
Overnight models are hinting at a break in the convection as the
secondary jet stream moves off to the north with negative vorticity advection prognosticated at the
500 mb level as the surface low lifts over the Soo. Even with these
factors there is abundant low level moisture across Southeast
Michigan...so a completely dry forecast is not in the cards and
neither is a continuation of the high probability of precipitation from today. With all
these factors in mind will maintain Chancy probability of precipitation during the overnight
hours. Abundant cloud cover and the region still in the warm sector
will once again lead to a mild night with overnight lows expected in
the 60s.
&&
Long term...Wednesday through Monday
Upper level troughing will keep mention of showers and thunderstorms
around into Thursday which is when the main trough axis passes east
of the area allowing heights to build. Meanwhile...complex surface low
pressure system will work through lower Michigan on Wednesday and Thursday
before a strong Canadian high pressure system drops into the Great
Lakes and expands across much of the eastern Continental U.S. For the Holiday
weekend. This will lead to a dry but cool weekend.
First off we will address convective potential for Wednesday. The
GFS poorly initializes the surface low over the northern plains so will
lean more toward the European model (ecmwf)/NAM/Gem regional. The upper level low
that has been sitting over the northern plains for a few days now
will phase with a northern stream trough digging south through
Manitoba/Ontario on Wednesday. This will lead to a more progressive
system finally. With the closed nature of the upper low...a few surface
lows have been rotating around each other the last two days. As the
wave opens further and the upper jet turns west/east across northern
Michigan...the main surface low will release and track across northern lower
Michigan through the day Wednesday. This will be a broad weakening low but
will present isentropic ascent and will keep the Theta-E ridge up
into Southeast Michigan. Focus will be placed on a southern stream shortwave that
will round the base of the trough and target lower Michigan Wednesday
afternoon. Model consensus shows a surface low clipping extreme Southeast Michigan.
This will open the door for additional heating and moisture into
that area during peak afternoon heating with the eastward tracking
upper level jet more squarely overhead. Convective parameters are on
the decline from Monday and Tuesday but there will still be 500 to
1000 j/kg of tall skinny MUCAPE with a cold/cool front passing
through the area in the evening. Overall Wednesday looks like it
will be composed of widespread showers and thunderstorms with a
chance of organized convection across the extreme southeast portion of the
County Warning Area.
Upper level trough axis will be over western lower Michigan Wednesday
night providing broad area of lift aloft with the back end of the
surface low still lingering. This will keep showers and thunderstorms
over much of lower Michigan through the overnight. The axis will sweep
through Southeast Michigan early on Thursday leading to a clearing trend in the
showers through the day from northwest to southeast. Main baroclinic zone thats
been lingering across the northern Great Lakes will surge south on
Thursday with strong Canadian high pressure right behind it. With
building heights aloft...clouds will clear out but that will not be
realized in temperatures. 850 mb temperatures in the low single digits will
only allow high temperatures to reach around 60f both Thursday and Friday
with lows around 40. A slow warming trend through the weekend will
only allow temperatures to rebound to near 70 for Monday and Tuesday.
Though it will be cool...at least it looks to stay dry thought the
Holiday weekend.
&&
Marine...
Modest southerly winds will remain in place today and Wednesday as a
low pressure system slowly lifts east out of the upper Midwest. A
warm and unstable environment will bring a chance of thunderstorms
during this time. Winds will shift to the north across all waters
by Thursday morning...as the low and trailing cold front push off to
the east. These conditions will push winds and waves close to small
craft criteria on Thursday over Lake Huron.
&&
Aviation...issued 1151 PM EDT Monday may 20 2013
//discussion...
The region of thunderstorms across Illinois will lift north-NE during
the early morning hours. Additional convective development is
possible out ahead of this cluster within a secondary surge in
moisture...traversing Southeast Michigan in the 09z to 15z time frame. This will
support the inclusion of some thunderstorms in the tafs around
daybreak. The coverage of morning convective activity and extent of
cloud cover which may linger into the afternoon raises considerable
uncertainty with respect to the chances and timing of thunderstorms
later in the day Tuesday.
For dtw...given the eastward extent of convection ongoing across
Illinois...chances of some thunderstorm activity in and around metropolitan
appear high enough to add their inclusion in the tafs during the 11
to 14z time frame. Although timing of additional thunderstorms later
in the day Tuesday remains highly uncertain...there is the potential
for several rounds of thunderstorms to impact metropolitan on Tuesday.
//Dtw threshold threats...
* medium confidence in thunderstorms Tuesday morning and afternoon.
&&
DTX watches/warnings/advisories...
Michigan...none.
Lake Huron...none.
Lake St Clair...none.
Michigan waters of Lake Erie...none.
&&
$$
Short term...kurimski
long term....drk
marine.......kurimski
aviation.....SC
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