Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260804_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.
925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date Time Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 08/04 12Z 0.64 3022 75 3 12 0.00
Tue 08/04 13Z 0.64 3123 70 2 12 0.00
Tue 08/04 14Z 0.63 3020 64 2 12 0.00
Tue 08/04 15Z 0.63 3017 59 2 12 0.00
Tue 08/04 16Z 0.64 2913 55 4 13 0.00
Tue 08/04 17Z 0.64 2812 59 9 13 0.00
Tue 08/04 18Z 0.81 2710 66 15 13 0.00
Tue 08/04 19Z 1.01 2610 69 18 14 0.00
Tue 08/04 20Z 1.24 2511 71 21 14 0.00
Tue 08/04 21Z 0.79 2510 68 26 14 0.00
Tue 08/04 22Z 0.47 2610 66 29 15 0.00
Tue 08/04 23Z 0.37 2609 63 33 16 0.00
Wed 08/05 00Z 0.30 2509 59 37 16 0.00
Wed 08/05 01Z 0.27 2509 55 38 17 0.00
Wed 08/05 02Z 0.26 2509 54 39 17 0.00
Wed 08/05 03Z 0.23 2508 54 39 18 0.00
Wed 08/05 04Z 0.22 2508 55 38 18 0.00
Wed 08/05 05Z 0.21 2507 56 38 17 0.00
Wed 08/05 06Z 0.22 2508 58 38 17 0.00
Wed 08/05 07Z 0.20 2607 58 39 17 0.00
Wed 08/05 08Z 0.18 2606 59 39 17 0.00
Wed 08/05 09Z 0.16 2605 59 38 16 0.00
Wed 08/05 10Z 0.17 2606 59 34 16 0.00
Wed 08/05 11Z 0.15 2605 60 27 16 0.00
Wed 08/05 12Z 0.14 2505 61 18 16 0.00
Wed 08/05 13Z 0.13 2405 62 12 15 0.00
Wed 08/05 14Z 0.13 2305 63 7 15 0.00
Wed 08/05 15Z 0.13 2205 64 5 15 0.00
Wed 08/05 16Z 0.15 2206 64 3 16 0.00
Wed 08/05 17Z 0.27 2307 65 2 15 0.00
Wed 08/05 18Z 0.31 2307 60 1 16 0.00
Wed 08/05 19Z 0.26 2306 52 1 16 0.00
Wed 08/05 20Z 0.26 2306 51 2 17 0.00
Wed 08/05 21Z 0.28 2407 53 3 17 0.00
Wed 08/05 22Z 0.28 2407 57 5 17 0.00
Wed 08/05 23Z 0.29 2508 64 6 16 0.00
Thu 08/06 00Z 0.32 2409 72 8 16 0.00
Thu 08/06 01Z 0.31 2509 74 12 16 0.00
Thu 08/06 02Z 0.27 2508 72 15 16 0.00
Thu 08/06 03Z 0.26 2508 70 22 16 0.00
Thu 08/06 04Z 0.27 2508 67 23 16 0.00
Thu 08/06 05Z 0.33 2509 68 28 16 0.00
Thu 08/06 06Z 0.38 2511 68 34 16 0.00
Thu 08/06 07Z 0.43 2512 71 44 16 0.00
Thu 08/06 08Z 0.42 2612 74 57 16 0.00
Thu 08/06 09Z 0.37 2611 75 57 16 0.00
Thu 08/06 10Z 0.32 2610 77 63 16 0.00
Thu 08/06 11Z 0.31 2610 79 64 16 0.00
Thu 08/06 12Z 0.25 2608 78 68 16 0.00
Thu 08/06 13Z 0.22 2606 78 77 16 0.00
Thu 08/06 14Z 0.16 2504 79 80 16 0.00
Thu 08/06 15Z 0.13 2204 81 76 16 0.00
Thu 08/06 16Z 0.17 2205 83 72 16 0.00
Thu 08/06 17Z 0.19 2104 83 66 16 0.00
Thu 08/06 18Z 0.29 2104 82 64 17 0.00
Thu 08/06 19Z 0.30 2104 81 62 17 0.00
Thu 08/06 20Z 0.19 2103 80 55 17 0.00
Thu 08/06 21Z 0.13 2004 80 52 17 0.00
Thu 08/06 22Z 0.16 2005 82 53 17 0.00
Thu 08/06 23Z 0.17 2006 83 46 17 0.00
Run total areal avg QPF for the greens is: 0.00 inches.
Froude Number (Frd#):
Frd# < 0.5 Flow is subcritical and blocked.
Upslope clouds/precip backed farther upwind of and up to mtn crest.
W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
Upslope clouds/precip falls immediately upwind of mtn crest.
W Upslope snow favors western slopes to the Green Mt. spine including:
Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
Gap winds possible.
Frd# 1-2 Flow is critical.
With strong winds, Mountain waves/downslope winds possible.
Precip falls close to mountain ridge crests and on lee side.
W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
Air flows freely over terrain.
Persistent upslope snow not favored. Scattered snow showers and flurries.
Relative Humidity (RH):
925-850 mb RH > 90% needed for upslope precipitation.
with 700mb RH > 70% favors upslope snow.
with 700mb RH > 90% greater amounts of W upslope snow possible.
850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
T > -11 10-15:1
T -11 to -15 25-35:1
T < -15 15-20:1