Area forecast discussion National Weather Service Marquette Michigan 501 am EDT Tuesday may 21 2013 Short term...(today and tonight) issued at 500 am EDT Tuesday may 21 2013 Upper air pattern consists of a closed 500 mb low over South Dakota with an associated trough over the northern and Central Plains...a 500 mb ridge over the lower Great Lakes and across the northern rockies. The 500 mb low moves slowly southeast this forecast period with the trough moving into the upper Great Lakes. Complicated forecast again today complicated further by a significant data outage that affected observation and computer performance. Anyway...trying to time out shortwaves moving through and kicking off convection will continue to be tough. There will be a wave of convection going through early this morning...then may see a brief break before more redevelopment as the morning GOES on. Think the redevelopment will be scattered probability of precipitation this afternoon. Will start off with categorical to likely probability of precipitation early this morning though. As for temperatures...again any sunshine that occurs has the potential to lead to a big forecast bust. Thinking is there could be a little sunshine along the Wisconsin border...but should not last that long to affect temperatures that much. Did keep lower 70s for highs today in that area with cooler temperatures elsewhere...especially near the Great Lakes shorelines. Chance probability of precipitation for tonight look to continue as the system weakens further and starts to drop a bit southward with time. Did not make too many changes to the going forecast for temperatures except to lower them a bit near the Lakeshore areas as water temperatures are still pretty cold. As for fog...kept the advisory going in the Keweenaw this morning as conditions do not change much with upslope moist flow off of Lake Superior. Rain that falls into Lake Superior will continue to cause upslope fog there for at least this morning. Long term...(tuesday night through monday) issued at 409 PM EDT Monday may 20 2013 The focus of the long term forecast this week will be the passing of a low pressure system across the Great Lakes region. Closed 500mb low over the northern plains this afternoon will make its way just south of Upper Michigan on Wednesday...gradually filling as it reaches the eastern Seaboard by Friday afternoon. This low extends from a trough associated with stronger low pressure situated over northern Quebec. At the 300mb level left exit region divergence has helped with the development of the low pressure system over the plains. This jet will shift northward and by Wednesday Upper Michigan will be slightly north of the best upper level support...in the right entrance region. 850-500mb qvector convergence shows best lift generally along southwestern-southern Upper Michigan/lower Michigan/Wisconsin accordingly. Meanwhile...a weak surface low developing in the plains moves northward along the trough...passing through lower Michigan and the lower Great Lakes Wednesday afternoon into Wednesday night. Model soundings show abundant moisture remains through all of Wednesday for central/eastern Upper Michigan before the very dry airmass/high pressure arrives Wednesday night/Thursday. Precipitable waters during this time still remain as high as 150 percent of normal. Have a diminishing trend for probability of precipitation from Wednesday afternoon Onward as dry air infiltrates the area and the surface low exits the region. Additionally...with abundant moisture in place expecting fog across Lake Superior and Lake Michigan for Tuesday night/early Wednesday afternoon. Once the drier air moves in the fog will dissipate. Upper level high over the Canadian prairie will sink southward and merge with the building ridge over the central United States on Thursday morning...bringing an end to precipitation for Upper Michigan. With dry air scouring out the clouds...northerly winds...and 850mb temperatures around 2-4c...Thursday afternoon looks to be mostly sunny with temperatures in the middle-upper 50s and maybe even low 60s....below normal by late may standards. Mixed layer dewpoints bring dewpoints into the upper 20s/30s which brings minimum relative humidity fields to 30-40 percent for middle afternoon on Thursday. A shortwave rotating around the 500mb low in Quebec will pass overhead Friday afternoon but with dry air firmly in place nothing will come of it beyond some scattered clouds. After Friday the upper level ridge will sprawl across much of the central and eastern United States. This will keep a drier airmass in place and keep conditions quiet through Saturday afternoon. A low pressure trough/shortwave will move into the Great Lakes area Saturday evening into Monday...bringing a chance for rain showers into the County Warning Area. && Aviation...(for the 00z tafs through 00z Tuesday evening) issued at 753 PM EDT Monday may 20 2013 Aviation forecast will continue to be challening through this period. With easterly upslope winds dominating at kcmx through the night...vlifr conditions will likely continue to prevail. May see some improvement Tuesday morning and maybe more so Tuesday afternoon as low-level winds back a little more to the NE and diminish the upsloping. Expect some rain showers at times...especially this evening and then Tuesday morning. At kiwd... rain showers over the next few hours will result in occasional MVFR conditions. Otherwise...VFR conditions should fall to MVFR than IFR overnight as winds shift to the NE...bringing cool/moist air off Lake Superior. May see improvement to low MVFR Tuesday afternoon. At ksaw...stratus patches lurking to the east and southeast should spread/expand northwest this evening as daytime heating comes to an end. Expect conditions to fall to MVFR then IFR by middle/late evening. Period of rain showers/LIFR conditions will occur late tonight/Tuesday morning as disturbance lifts NE into the upper lakes. With NE winds during the day Tuesday...may not see conditions improve above IFR at ksaw. && Marine...(for the 4 am Lake Superior forecast issuance) issued at 500 am EDT Tuesday may 21 2013 The main threats through the period marine wise will be the northwest winds funneling over Western Lake Superior...with gusts of 20-30kts through this evening. The second threat will be the continued fog that will likely linger into Wednesday morning...when drier air works in from the north-northwest. Low pressure over S Minnesota will cross into Wisconsin and Northern Lake Michigan this evening...before exiting across lower Michigan and the lower Great Lakes Wednesday and Wednesday night. In the meantime strong...dry...and cool high pressure over north Canada is expected to sink southward. The result will be lighter winds as a ridge moves overhead on Thursday and builds slightly on Friday. The ridge will likely linger across the Great Lakes region through at least Saturday. && MQT watches/warnings/advisories... Upper Michigan... dense fog advisory until 11 am EDT this morning for miz001-003. Lake Superior... dense fog advisory until 8 PM EDT this evening for lsz243>249- 263>267. Dense fog advisory from 8 am EDT /7 am CDT/ this morning to 8 PM EDT /7 PM CDT/ this evening for lsz162. Gale Warning until 8 am EDT /7 am CDT/ this morning for lsz162. Lake Michigan... none. && $$ Short term...07 long term...mesoscale discussion aviation...rolfson marine...kf