Flow Channeling in the Mohawk & Hudson Valleys

1. Flow Channeling in the Mohawk & Hudson Valleys A FURTHER INVESTIGATION OF MOHAWK HUDSON CONVERGENCE Tenth Annual Northeast Regional Operational Workshop/NWS/CESTM Hugh W Johnson IV Lance F. Bosart Michael E. Augustyniak

2. Geography of New York & New England

3. Geography of New York & New England

4. Definition • Mohawk-Hudson Convergence occurs when surface air parcels traveling down the upper Hudson Valley (from north to south) meet air parcels traveling down the Mohawk Valley (from west to east) • The convergence of these airflows can generate vertical motion and precipitation (usually in the general vicinity of Albany)

5. WHY PURSUE MHC CASES ? • OPERATIONAL IMPACT WITH REGARDS TO HIGHWAY CREWS • IFR AVIATION ISSUES • PUBLIC PERCEPTION • POSSIBLY FOCUS FOR THE INITATION OF CONVECTION

6. IN ADDITION • WILL EXAMINE NOT ONLY THOSE CASES WHERE A NORTH WIND PERISTS IN THE HUDSON VALLEY WHILE THE WIND BACKS TO THE NORTHWEST OR WEST IN THE TERRAIN WEST OF THE HUDSON VALLEY… • BUT ALSO EXAMINE A CASE WHERE THERE IS A SOUTHERLY FLOW IN THE HUDSON VALLEY WHILE A WEST OR SOUTHWEST WIND PREVAILS TO THE WEST

7. THANKS TO MIKE WE HAVE A DECISION TREE THAT IS READY TO BE USED THIS WINTER

8. Is ∆p KGFL-KPOUbetween 1 & 5 hPa and ∆p KRME-KPSF greater than 4 hPa? YES Will a surface low pass east or south of the 40°N- 70°W benchmark? NO YES NO Will synoptic forcing in the vicinity of KALB be weak? Mohawk-Hudson Convergence Not Likely YES NO NO Is weak low-level CAA expected? NO Is a north-to-south 850-hPa WFROPA forecast? YES YES Is moisture trapped under a low-level inversion or isothermal layer? YES NO Mohawk-Hudson Convergence Is Likely Mohawk-Hudson Convergence Not Likely

9. LOOK FIRST AT A “CLASSIC” CASE ON JANUARY 2, 2008

10. 09Z SFC PLT 01/02/08

11. 11Z SFC PLT 01/02/08

12. KENX 0757Z

13. KENX IMAGE 0930Z

14. KENX 1151Z

15. SUNRISE RADAR 1230Z

16. KENX 1259Z

17. 1659Z KENX

18. 12Z ALY RAOB

21. SUMMARY… • PROLONGED MHC WITH SEVERAL PULSES OF EPISODES • WIND MOSTLY NE AT KGFL/N AT KALB/NW KUCA(KRME) • SNOWFALL RATES UP TO AN INCH PER HOUR OBSERVED • VERY HIGH SNOW TO LIQUID RATIOS • NAM NOT PERFECT • UNDER AN INCH CESTM/OVER AN INCH MY HOUSE/2+ INCHES BRUNSWICK • JACKPOT= 5.2 INCHES IN COHOES!

22. SECOND CASE…A NULL CASE • ST. PATTY’S DAY STORM OF 07 • LOTS OF SNOW • BUT VERY LITTLE MHC • DID NOT MEASURE AT THE AIRPORT OR CESTM

23. SAT MARCH 17 2007

24. 08Z SAT MAR 17 2007

25. 0914Z MAR 17

26. 0943Z 17 MAR

29. 08Z SFC PLOT AGAIN

30. SUMMARY • SOME BRIEF MHC • THE WIND WAS MOSTLY NORTH AT KGFL AND TO THE WEST • NO MEASURABLE AT ALBANY • IMPLIES VERY LITTLE IF ANY CONVERGENCE • WHY DID THIS HAPPEN???

31. HYBRID CASES • OCCUR WHEN A SECONDARY SHORT WAVE MOVES THROUGH THE BACK OF THE MAIN TROUGH • FEB 27 2008 BEST EXAMPLE …COMBINED MHC AND SHORT WAVE HAD IT SNOWING ALL DAY (LIGHTLY) EVEN THOUGH SURFACE CYCLONE PAST THE GULF OF MAINE

32. FINALLY WE WILL TAKE A LOOK AT CASE WITH A SOUTHERLY FLOW IN THE HUDSON VALLEY AND A SOUTHWEST WIND IN THE MOHAWK VALLEY JUNE 22 2008

33. SFC PLT 15Z 06/22/08

34. 0.5 KENX BASE REFLECTIVITY LOOP FROM 9-10 AM 0.5

35. 0.5 BASE REFLECTIVITY KENX RADAR LOOP 2-3 PM

37. 0.5 BASE KENX REFLECTIVITY 3-4 PM

38. IN SUMMARY • SOME EVIDENCE SUPPORTS POSSIBLE MHC FROM WITH A SOUTHEAST WIND HUDSON VALLEY/SOUTHWEST WIND MOHAWK VALLEY • 850 WINDS ESTIMATED TO BE ONLY 15-20 KTS AND 925 WINDS AROUND 10KTS

39. IN ADDITION… • WRF WAS NOT AVAILABLE • NAM DID NOT HANDLE LOW LEVEL WIND FIELD WELL • DID NOT INDICATE SE WIND IN THE HUDSON VALLEY AND SW IN MOHAWK (HAD EVERYONE SOUTHWEST) • MANY MORE CASES NEED TO BE EXAMINED

40. PLAN TO CONTINUE TO EXAM PAST AND FUTURE MHC CASES AS AND SEE HOW THE WRF HANDLES THEM

41. CONCLUSIONS • MHC COMES IN MANY FLAVORS (NOT AS MANY AS BEN AND JERRY’S) • MODELS USUALLY HAVE A “CLUE” BUT NOT ALWAYS • NEED TO SEE HOW WELL MIKE’S CHECKLIST WORKS FOR THE UPCOMING WINTER SEASON • SEE HOW THE WRF DOES

42. Thank You! Questions?