May 21-25 Potential Storm System & Severe Weather

I'm analyzing the May 21-25 time period for a substantial storm system to bring cool weather and possibly some severe weather to the nation.

Tropical Tidbits

The image above shows projected 500mb height anomalies over the western Pacific. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. Looking towards Japan on this forecast graphic, valid on May 15th, we see a substantial closed low approaching Japan, bringing in cooler than normal and unsettled weather for the area. If we utilize the Typhoon Rule, we can expect this storm system to impact the United States 6-10 days after this storm affects Japan, which would give us a May 21-25 time period.

Indications I am getting from this graphic tell me much of the United States may be impacted by this cooler than normal weather, and while I do believe severe weather is possible, I'm currently thinking any severe weather will be limited due to the lack of a powerful ridge advecting north over Japan prior to this closed low hitting the country.

Andrew

Cool, Stormy Weather To Give Way to Summery Warmth by Late May

I'm expecting some cool and stormy weather in mid-May to eventually give way to a shot of above-normal temperatures, before a cool spell returns for late May.

* A quick note, I have had at least 8 comments telling me that my late April-early May forecast was wrong, with more than a couple of these comments delivered with a less-than-enticing attitude. I've been receiving these comments for 2 weeks now- enough is enough. I don't expect myself to be correct 100% of the time, and I certainly hope no one else expects that of me, either.

Tropical Tidbits

The latest GFS Ensemble forecast above, valid on the evening of May 6th, shows troughing and cool weather present over Japan. By using the East Asia / Typhoon Rule, we can estimate that cool and stormy weather is can be expected around May 13-17th or so. Judging by the weak negative 500mb height anomalies, I'm only expecting a weak chill in the US, with the strongest cold weather allocated further north.

Tropical Tidbits

By the morning of May 9th, we see that the western portion of that elongated trough, seen in eastern China on the first image we analyzed, as now become a closed low and is progressing through Japan. If we once again apply this correlation, it is understood that a strong closed low may traverse the United States between a May 15-19th period. When this low comes through, I'm estimating we see it hit primarily the northern and central thirds of the nation, if you were to slice the US into thirds, horizontally. Cooler than normal temperatures can be expected with this, as well.

Tropical Tidbits

We finally do get relief in mid-late May, we a massive ridge of high pressure pumps up over Japan on May 11th, sticking around for a little while. This tells me we can then anticipate a period of anomalously warmer than normal weather in the United States around May 16-22nd or so.

Tropical Tidbits

Unfortunately, long range ensemble guidance supports the return of troughing and associated cold weather in Japan by May 16th, leading to potentially cooler and stormier weather in time for Memorial Day weekend.

Andrew

May 7th-8th Potential Severe Weather Threat

It's looking more like we can expect a severe weather threat around the May 7th-8th period.

Tropical Tidbits

(The following is copied from a May 1st post) On the afternoon of May 2nd, we see a small but still-substantial ridge of high pressure pushing over Japan, as a strong storm system to the west begins pushing in the direction of the island nation. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. Seeing as this ridge appears on May 2nd in Japan, we can expect some warm weather around May 8-12th.

Tropical Tidbits

By May 3rd, we see a strong storm pushing into Japan in the wake of the ridge we saw in the image above. Looking at the trough, it looks like the system is negatively tilted, as seen by the pressure contours pushing in a south-east direction. If this trough reflects on the United States in about a week, which it very well may, the negative tilt may result in a pretty substantial severe weather threat. Locations of this threat are unknown at this time, but be cautious for some severe weather in this timeframe. (End copied portion)

The Storm Prediction Center has outlined an area of enhanced severe weather risk on May 8th from Oklahoma into southern Wisconsin. This threat area includes cities such as Chicago IL, Milwaukee WI, and Wichita KS, just to name a few. 

The surface analysis forecast from the Weather Prediction Center for May 8th shows a strong low pressure system moving northeast into Minnesota, dragging a warm front to the north, which should allow for a warm, moist and unstable atmosphere to flow over the area. To the west, we see a cold front draped across the Central and Southern Plains, with a dryline denotation in western Oklahoma and Texas. I expect that we will see the cold front be the main cause for this severe weather event, while the dryline to the south may provoke additional activity in the southern Plains. I anticipate the highest tornado threat to remain in the southern Plains, as dryline features typically can retain more tornadic cells than cold fronts, but we will analyze that idea later on. The Storm Prediction Center indicates we can expect the main threats to include damaging winds and hail, with a tornado threat still present, as is indicated below.

AS MODELS BRING THE UPPER TROUGH EWD INTO THE PLAINS DAY 6 /THU 5-8/
   HOWEVER...MORE COMPLETELY MODIFIED GULF MOISTURE APPEARS LIKELY TO
   HAVE SPREAD INTO THE CENTRAL U.S. PERMITTING DEVELOPMENT OF MORE
   SUBSTANTIAL CAPE.  AS THE SURFACE LOW SHIFTS NEWD ALLOWING A
   TRAILING FRONTAL ADVANCE ACROSS THE CENTRAL PLAINS
   VICINITY...DEVELOPMENT OF AFTERNOON SURFACE-BASED STORMS APPEARS
   LIKELY.  WITH THE GREATEST JUXTAPOSITION OF FAVORABLE SHEAR AND
   MODERATE CAPE LIKELY TO EXIST FROM ROUGHLY OK NEWD ACROSS KS/MO/IA
   AND INTO IL AND SRN WI...IT APPEARS THAT INCLUSION OF A 30
   PERCENT-EQUIVALENT RISK AREA CAN BE INTRODUCED ATTM WITH MODERATE
   CONFIDENCE...WITH HAIL/DAMAGING WINDS LIKELY ALONG WITH SOME TORNADO
   POTENTIAL.

I do believe we may see another severe weather outlook posted for May 7th for areas further to the west, as we take a look at rank-analog tornado probabilities off of the GEFS modeling system. Out of the four panels, the one which highlights the overall tornado probability is in the top-left corner, and we can see in that panel that Nebraska and Kansas may be in line for as high as a 10% chance of a tornado, which would certainly warrant a severe weather outlook.

If we take a look at the same four-panel forecast image, now valid on May 8th, we can see how the Storm Prediction Center is highlighting areas in Oklahoma into Wisconsin. It appears that the tornado threat here is weaker and displaced farther west than the SPC outlook for this day, but as was mentioned earlier, the main threats should be damaging winds and hail. I find that the threat for this day is more accurately highlighted in the other three panels, which calculate different values for ingredients of severe weather and general thunderstorms.

Overall, we are looking at a severe weather threat on May 8th (and potentially May 7th) over the Plains and Midwest regions.

Andrew

Long Range Forecast Update for Late April, Early May

This is an update to a previous long range outlook concerning the expected weather for late April and into early May.

Tropical Tidbits

For the last days of April and in to early May, I'm still looking at above normal temperatures for a decent portion of the nation. Shown above is the 500mb height anomaly pressure forecast over the West Pacific for April 26th. In this image, we see a strong ridge of high pressure stationed over Japan and East Asia, permitting the flow of above normal temperatures into the area. This event has significant implications on our weather here in the US. There is a rule, well explained by Joe Renken, that states a weather phenomenon in East Asia will be reciprocated in the United States 6-10 days later. This means that if there is a storm system in Japan on a certain day, we can expect a storm in the US 6-10 days after that. The same goes for high pressure and warm weather. So, if we use that rule, we can expect warmth over the United States around the May 1-5 period, if not for a longer time period than that. 

Tropical Tidbits

By the end of the first week of May, I anticipate that we will see another cool-down for a few days as a closed low looks to move into Japan. Since this 500mb anomaly image is valid for April 29th, we can expect this cool-down to start showing itself sometime around the May 4-8 time period, though the timeframe could probably be extended to May 4-10 as the closed low sticks around Japan for a day or two more. Despite how long that timeframe may seem, the actual cold weather should only be around for a few days, not for this whole 6-day timeframe.

Tropical Tidbits

By the time we get to the second week of May, we're looking at another bout of sustained warmth, as the GFS ensembles bring about a ridge of high pressure over Japan and the waters surrounding the island nation. Ensemble guidance looks to have rather low confidence in this event, though we should get a more accurate look at this portion of the forecast in the next few days. 

To summarize:
• I am still forecasting warmer than normal weather for the last few days of April into very early May.
• Cooler weather looks to take hold near the end of the first week of May.
• Warm weather may return for the second week of May.

One final note, I received a multitude of arrogant responses to the previous long range outlook I had posted. Remember that every comment is moderated before it's published, and arrogant comments like the ones I've been getting for the last few days will not be published.

Andrew