After unsettled conditions at the start of the week, we will get into a drier stretch of weather which (at the time of this Sunday night posting) should extend from at least Tuesday afternoon into Saturday. Following passage of a cold front, temperatures will be on the Seasonably Cool side into Wednesday evening. A large ridge of dry high pressure will bring us abundant sunshine Wed-Saturday (excluding nights! ). Readings will begin to move back up on Thursday, and go above average on Friday into Sunday. During the weekend, humidity will increase, and a few Shwrs & Tshwrs will begin to come back into the picture, possibly Saturday night and more likely on Sunday.
Following this peak warmth, temperatures will become more moderate again, as the warm ridge of high pressure begins to drop away from us. Most ensemble means show the peak ridging and warmth returning to the western US, but these means only allow modest cooling in the Great Lakes which would bring temperatures back to near normal, rather than below normal/average. It’s difficult to discern whether or not our precipitation will go back to above average during that transition. But it does appear our Tue afternoon-Saturday dry “spell” will help get some meaningful evaporation going in the muddy fields.
In the mean, the pattern will continue to favor below average temperatures and above average precipitation for the Great Lakes and nearby regions. We will have a ridge of high pressure over the west central US, with a trough in the west and a trough over the NE. That favors a NW flow at mid levels of the atmosphere which will deliver disturbances and relatively cool temperatures.
However, it should be remembered that this is a Mean pattern to which I refer. It doesn’t mean we won’t get some warmups and some drier periods in the 2nd half of the month. But when a Mean is so well established, it’s hard for a fundamental pattern shift to gain traction with higher soil moisture and the resulting cooler boundary layer/near surface temperatures.
At the time of this posting–Tuesday night–it still appears a strong (for mid June) area of low pressure will do its worst in the Ohio Valley & PA, rather than in our viewing area during late Wed night into Thursday morning. This storm system will probably spawn a complex of long-lasting violent tstorms Wednesday night. The modeled most likely position of this low would steer such a complex (which may become a powerful derecho (http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm) from Illinois into PA and possibly parts of VA. We will be monitoring this storm system, in the event there is a northward shift in its projected path.
We will be drying out during a Cool Friday into a lovely Saturday. Sunday holds some question. One NWS global model (known as the GFS/Global Forecast System) brings showers into WNY during Sunday, giving us only one nice weekend day. However, the usually (not always) superior European global model keeps us dry through Sunday. Owing to its superior performance, I will go with the European on this Tuesday evening for next Sunday. Either way, even if we get 2 great weekend days there are still no signs of an extended dry period or true summerlike heat returning anytime soon.
Obviously, the heat is gone this week. But there are signs that June may end up being cooler more often than the very warm May we just finished. Certainly, there will be warm periods, but the overall pattern and another oscillating pattern favor more frequent troughing over the midwest and the NE, with the strongest/warmest ridging staying over the SW. That is a mean, and will be interrupted to be sure by variations in the pattern. But if this mean were to verify, it also would favor a wetter than average month. Having said all this, it’s only June 3rd as I post this…so much of it is subject to change.
Later this week, tropical moisture is likely to sweep up from the Gulf and SW Atlantic into the east & NE, with some of it arriving in bits and pieces before Thursday morning, and increasing into Thursday-Friday. There will be occasional rounds of showers & tshowers. Currently, the heaviest rain is likely to fall just east of us, but that’s cutting it a little close. Abundant cloud cover should keep instability limited, which makes severe tstorms unlikely. Some of this wet period may linger into a portion of Saturday, with Sunday being the nicest of the 2 weekend days. Another area of low pressure will begin to increase the likelihood of scattered showers by Monday afternoon. Some overall moderation in temperatures should be setting up by mid month. But as of this posting, there are no signs of a return to mid 80s-type heat in the ensemble means.
As our airmass draws higher dewpoints into the region, the trigger mechanism for any tshowers on Monday afternoon will be the edge of a weak Lk Erie breeze over the hilly terrain well inland to the S & SE. There will be several rounds of convection Tue-Wednesday night, with the atmosphere ripening for somewhat more widespread coverage, especially later Tue and Wed. Winds aloft will be fairly weak, meaning tshowers & more vigorous tstorms will tend to be slower-moving. A few spots could receive gullywashers and experience poor drainage flooding. In addition, this will be our first stretch of Sticky Days and Nights, lasting into Wednesday evening. SPC has WNY at Slight Risk for Severe on Wednesday. Some of that risk will depend on how much destabilization we do or don’t get from solar heating. Modeled profiles suggest some low level directional shear on Wednesday, with winds veering from SSW to SW with increased height. Still, the models as of Monday morning don’t suggest a particularly potent setup…we’d need some less than likely widespread sunshine and a little more shear than what’s expected as of this Monday AM to make things really pop.
By Thursday, we’ll be on the cooler side of this wavy front, with scattered showers. Cool & Dry air will move in for Friday, with daytime highs only in the low 60s and not much warmer on a bright & sunny Saturday. We should be back to the mid and upper 60s by Sunday, and getting closer to 70 for Memorial Day. I can’t rule out some patchy valley frost Friday and/or Saturday night.
After the frosty start to this week, a warm front will arrive in WNY by Wednesday AM, ushering in some Sct Showers & Tstorms. This will be elevated convection, so it will not be impacted by the cooler lake waters. The models for wind directional change with increased altitude show quite a bit of low level veering/wind shear, so some thunderstorms with rotation can’t be ruled out. After one or 2 rounds of Sct convective cells into early Wednesday afternoon, things should settle down for a few days, with daytime highs averaging in the low 70s. The chance for Sct convection will probably return by Sunday into Monday and Tuesday. The airmass at that time will be warm and instability will be on the increase. An upper level trough may take on an orientation (negative tilt showing in some ensemble means) which would increase advection of warm & humid air and help create better dynamics for strong tstorms by Tuesday. A cold upper level low well to the NW of the surface low will feed cold air aloft and create more impressive lapse rates.
It’s VERY early in the game, but this kind of pattern can be recognized as one which can increase the chance for severe tstorms over parts of the Great Lakes.
Our streak of 70+ degree days reached 7 as of Monday, and a few more are likely to keep that streak going. A slow moving storm system over the south will send some very limited moisture into WNY on Wednesday. In the meantime we also had 5 consecutive days with 100% of the possible sunshine 5 days in a row…rare ’round these parts! A few more spotty showers may be around on Thursday and Friday as well. During Saturday, a cold front will drop into the Great Lakes. The rainfall potential with this strong front remains quite uncertain, but Sunday/Mother’s Day will probably be our first day with below average temperatures in 2 weeks. A few showers may pop up with the cold air aloft producing some instability on Sunday, but it should be rainfree most of the time. Sunday night could bring some patchy frost inland IF skies clear enough and winds subside sufficiently. Monday will still be cool, but plenty sunshine will return, and readings will go back to above average by Wednesday. So, this chillier period is going to be strictly a quick hit.
There is no real confidence any longer that early CPC outlooks for a milder than average spring will bear fruit in May. In the near term, although the CPC is giving us a somewhat positive anomaly for temperatures in the 6-14 Day Outlooks, it should be noted that the 3 indices will be trending in the wrong direction for significantly warm anomalies around here. The AO and NAO are both showing most of their ensemble members trending toward negative territory in May, while many PNA members trend upward. While these indices tend to have a little less impact climatologically as we move into mid-spring, this year that may not be so much the case. A major snow cover anomaly continues over much of the northern plains and nearby Canadian praries, assuring a colder pool of air. That, plus a large area of high soil moisture will also hold temperatures down. Whether these anomalies will still play a key role later in May is unknowable right now.
The MJO has become weaker, and its climatological impact also lessens as the month goes on. ENSO remains neutral, and is forecast by most models as likely to stay neutral through the autumn.
While these near term positive temperature anomalies are the first we’ve seen from CPC in probably a couple of weeks for us, the confidence level for both the 6-10 & 8-14 Day Outlooks is only 2 out of 5, and that may be tied partially to the indices’ trends I outlined above.
In any case, CPC has backed off from the weak warm anomaly it had for our region for May, and gone over to EC. And, since ensemble means are showing no rebuilding of an eastern ridge with any staying power in the next 14-16 days, I concur with that call.
After this past week’s soaking rain, I wouldn’t say there’s “no rest for the weary”, but there may not be enough rest. A strong warmup on Monday from a downslope wind will boost temperatures by close to 20 degrees from Sunday’s high. The proximity of a nearby cold front will increase the chance for some showers by Tuesday, but the amount of rainfall we can expect from the passage of that front seems uncertain. Later in the week, the European model brings a deep low pressure system toward the northern Great Lakes. That might warm us up again sharply around Thursday, but the Gulf inflow ahead of its cold front and the dynamics of that storm–if realized–could bring convective rains and the potential for larger amounts. A backslide will arrive by or during Friday to below average temperatures into the weekend. The ensemble means are not showing much in the way of a rebuilding of a warmer pattern afterward, into the following week.
The indices seem to support that cooler pattern again as well, with the AO ensemble trending downward later in the month. The NAO has a lot of spread, but there appears to be a slightly negative mean to the ensemble members. And, there is an upward tick in the PNA members at the very end of the 14 day period.
The anomalous snow cover over the upper plains/upper midwest and Canadian prairies is also serving as an anomalous cold air reservoir for the north central US, and that reservoir can also deliver chilly outbreaks to us–as we already know.
Pretty harsh afternoon for the Dyngus Day parade, with a nasty wind chill, some bits o’ sun, and some occ’l snow showers. The hills well south could see 1-3″ amounts overnight, with a little blowing snow to boot. But there are FINALLY signs of a more fundamental pattern change taking shape gradually later this week and continuing into next week. For example, the European 500mb ensemble mean shows rising heights in the east and falling heights in the interior of the west. This would allow temps to approach age at the end of the week and to run somewhat above average much of next week. There’ll be some ups and downs here and there, but MEAN is changing. Average high for today is 48
As forecast last week, conditions this week are a good deal less harsh. But daytime highs will continue to run below average for the remainder of the work week, with a temporary moderating trend during the weekend. The North Atlantic block which has forced the polar jet stream to buckle to the south from the northern plains to the mid-south and up through the interior of the NE is weakening, but not entirely dissipating. Some nuisance snow showers will show up Wednesday into Thursday. The high angle of the sun will likely mix the snow with some rain during the afternoon at lower elevations. After high pressure moves in to bring us a pleasant Saturday, a warming downslope breeze will develop Saturday night into Easter morning ahead of another cold front. While temperatures will move above average for much of Easter, rain showers will develop by afternoon. After that sharp cold front goes by, however, we take 2 steps back with a gusty wind and falling temperatures on Monday–and the redevelopment of snow showers. No major storms are in sight, but we’ll have to keep an eye out for lapse rates/instability over the Lakes early next week, as some lake effect cannot be ruled out. Temperatures will run below average during the work week.
In the longer term, ensemble means (European, GFS, and Canadian) all seem to show more “tolerable” temperatures further out in time. There are still no signs of a fundamental shift to a western trough/warming eastern ridge, but the flow does seem to become nearly zonal in the mean. This would allow temperatures to be closer to average. The MJO is favored to become somewhat less active, which would favor greater variability over the North Atlantic (source: CPC), and the AO and NAO stay negative, but at much less amplitude. The PNA is looking to be more neutral. In the mean, it looks like a flatter pattern. However, interactions with individual short waves–as always–cannot be seen in this time range.