Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
641 FXUS63 KMQT 191950 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 350 PM EDT Sun May 19 2024 .KEY MESSAGES... - Borderline elevated fire weather conditions today with warm and very dry conditions, but winds on the lighter side. - Showers and isolated thunderstorms Monday, especially in the morning and early afternoon. - Strong storm system will bring rain and thunderstorms late Tuesday into Tuesday night. - Windy conditions develop behind the system on Wednesday. && .SHORT TERM /THROUGH TONIGHT/... Issued at 336 AM EDT Sun May 19 2024 Today, sfc high pres ridging and an associated very dry air mass will build into the Upper Great Lakes in the wake of last night`s frontal passage. Full sun thru the morning will give way to thickening mid/high clouds arriving from the w in the mid-late afternoon ahead of a weak shortwave rippling thru the mid-level ridge. Strong insolation will result in deep mixing into extremely dry mid-levels. NAM soundings show late morning dewpoints at 800mb/~5kft AGL ranging from -20 to -40C, though this is the low end of the model guidance. Even though moisture aloft does increase during the afternoon, mixing potential still supports sfc dewpoints falling thru the 30s F. Some locations will see upper 20s F. The low dewpoint potential is also evident thru the local mixed dewpoint tool and simply in some of the raw model guidance, which the HRRR appears to capture quite well. With high temps fcst in the mid/upper 70s F across the interior, the low dewpoints will drive RH down to around 20pct across much of the interior of Upper MI this afternoon. The good news is winds will be on the lighter side, though a little higher than previously expected. Sustained winds will be around 10 mph with gusts to around 15 mph. Winds will be strongest across the Keweenaw where gusts to around 25mph are possible. Lake breeze development should help limit fire wx concerns close to the Great Lakes shorelines due to cooling conditions (temps falling into the 60s F), and higher dwpts, resulting in higher RH. && .LONG TERM /MONDAY THROUGH SUNDAY/... Issued at 350 PM EDT Sun May 19 2024 Southwesterly midlevel flow between deepening troughing over the northern/central Rockies and ridging extending form the Deep South through the Northeast will result in the preferred storm track being located over the local area through midweek. This will lead to periods of rainfall through at least Wednesday. Shortwave ridging favors a drier period to end the week Thu/Fri, with precip chances reentering the picture to start the holiday weekend Saturday. Aside from a brief cool-down Thursday, temperatures look to average near to slightly above normal for the upcoming week into the start of next weekend. Initial shortwave of concern looks to touch off convection over the Central Plains today, and may itself be convectively enhanced as it ejects northeastward to the upper Great Lakes by Monday. Low-level jet strengthening to 30-40 kt at 850 mb will enhance moisture transport into the region, with PWATs increasing to 1.25-1.50 inches, or +1 to +2 stdev. High confidence in an area of rainfall continuing over the western UP by the start of the period (12Z/7 am CDT Mon), continuing into the central UP by mid-morning, and likely reaching the eastern UP by early afternoon. Although a couple rumbles of thunder will be possible, the corridor of better instability should remain well to the south. Confidence is lower on what happens during the afternoon and evening hours. It`s reasonable to expect some subsidence on the back of this initial wave to dry things out for the afternoon, especially west/central. However, some CAMs, namely the 12Z.19 NAM3 and HRW-ARW have a trailing convectively- generated wave bringing in another round of rainfall for the afternoon central and east. Reduced PoPs a bit here for the afternoon/evening as I feel that this scenario is not the most likely. Forecast soundings suggest some lower clouds may linger through the day which would limit surface-based instability to redevelop; however, should the convectively generated wave materialize, some elevated convection would be possible. Monday night should be quiet and partly to mostly cloudy in the wake of Monday`s rain. Tuesday morning will start out quiet, then attention turns to the highest potential impact portion of the period, late Tuesday into Wednesday. The culprit is a negatively tilting, vigorous shortwave trough ejecting out of the central Plains into northern MN/Lake Superior. This will foster an unseasonably strong cyclone. The 00Z NAEFS mean has this low bottoming out at 996 mb near the Keweenaw at 12Z Wed, which is below the 1 percentile relative to climatology. However, the 12Z EPS/GEFS mean have this low at 992 mb, and several members (and the 12Z ECMWF) have this low down in the mid/lower 980s, which is highly anomalous for this time of year. There is still considerable uncertainty on the track, with generally a stronger storm favoring a westward and slightly slower track. Regardless, this storm will feature incredibly strong dynamics and moisture transport, with PWATs likely above 1.50 inches Tuesday night. Showalter values go negative Tuesday night as steeper midlevel lapse rates move in. With at least modest instability coupled with very strong wind shear, there is potential for large hail along with heavy downpours, as SPC has included portions of the central and southern UP in a Slight Risk (level 2/5). Thinking it`s unlikely that we get into the warm sector with model soundings showing convection being elevated, especially as the strongest forcing is likely to arrive after sunset, so wind threat is more uncertain at this time. Heaviest rainfall looks to favor the western UP, with EPS probabilities of 2"+ at 20-30%. However, potential for a more widespread flooding event should be mitigated due to ongoing drought conditions in the region. A westerly track of the system (e.g., 12Z ECMWF) would open the door for synoptic-scale wind concerns on Wednesday in the favorable location beneath the midlevel dry slot. If low-level moisture scours out, strong mixing could occur and tap into the strong low-level wind field. ECMWF EFI values exceeding 0.8 signify potential for unusually strong winds. EPS mean wind gusts are widespread 40 kt here. Something to monitor in the coming days, and will wait until storm track becomes more certain to message this threat more strongly. Cold advection on the back side of this system will keep things on the cool and dry side for Thursday, with a modest warming trend Friday and the next system possibly (40-60% chance) bringing rain back Friday night into Saturday. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 225 PM EDT Sun May 19 2024 VFR cigs/vsby prevail through this evening at all terminals. Gusty west winds continue at CMX until closer to sunset when light and variable winds spread across all terminals. Conditions deteriorate late tonight into Monday morning as a wave of rain and perhaps a few embedded thunderstorms lifts north across Upper Michigan. Model guidance drops cigs down to IFR/LIFR on Monday as this area of rain moves through and am most confident in this occurring at CMX/SAW due to east/southeasterly upslope flow. && .MARINE... Issued at 350 PM EDT Sun May 19 2024 With the exception of some locally higher gusts of 20-30 kt along the tip of the Keweenaw and in the vicinity of Isle Royale through early this evening, winds should remain around 20kt or less through Tuesday morning. Main period of interest is Tuesday afternoon through Wednesday as an unseasonably strong low pressure system tracks from the central Plains across Lake Superior and into southern Ontario. There are still important model differences that will dictate peak wind speed and direction, but right now the highest probabilities for northeasterly gales are Tuesday night over the western and north-central part of the lake, with 30-60 kt probabilities here. Winds remain elevated as they shift to a westerly component on Wednesday with 25-30 kt expected. If the low track ends up being further west than anticipated, Tuesday night northeasterly gales would be less likely, but Wednesday southwesterly gales would be more likely, possibly lingering into Wednesday night. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...Thompson AVIATION...EK MARINE...Thompson