Subject: NAM3 EXPERIMENTAL Froude Number for the greens
Model run: BTV_GRID_D2D_NAM3_20260528_0000
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)
=== ===== === ==== ==== === === === ====
Thu 05/28 00Z 0.07 3512 74 89 10 0.00
Thu 05/28 01Z 0.05 3514 72 81 9 0.00
Thu 05/28 02Z 0.06 0014 72 86 9 0.00
Thu 05/28 03Z 0.12 0113 75 88 8 0.00
Thu 05/28 04Z 0.10 0112 78 93 8 0.01
Thu 05/28 05Z 0.07 0011 80 89 7 0.00
Thu 05/28 06Z 0.04 3511 84 89 7 0.00
Thu 05/28 07Z 0.07 3511 84 84 6 0.00
Thu 05/28 08Z 0.09 3513 86 82 6 0.00
Thu 05/28 09Z 0.11 3514 88 76 5 0.00
Thu 05/28 10Z 0.09 3516 90 73 5 0.00
Thu 05/28 11Z 0.08 3516 91 70 4 0.01
Thu 05/28 12Z 0.11 3516 93 69 4 0.01
Thu 05/28 13Z 0.16 3416 92 67 3 0.00
Thu 05/28 14Z 0.42 3417 91 65 3 0.00
Thu 05/28 15Z 1.26 3318 89 65 3 0.00
Thu 05/28 16Z 1.98 3320 88 64 3 0.00
Thu 05/28 17Z 2.29 3420 86 63 3 0.00
Thu 05/28 18Z 1.81 3319 88 69 3 0.02
Thu 05/28 19Z 2.14 3320 89 70 4 0.01
Thu 05/28 20Z 1.81 3322 90 66 4 0.02
Thu 05/28 21Z 1.22 3323 90 61 4 0.01
Thu 05/28 22Z 0.68 3325 92 69 4 0.02
Thu 05/28 23Z 0.45 3426 92 62 3 0.02
Fri 05/29 00Z 0.33 3425 92 47 3 0.01
Fri 05/29 01Z 0.28 3424 93 39 3 0.00
Fri 05/29 02Z 0.28 3424 92 35 2 0.00
Fri 05/29 03Z 0.29 3424 91 38 2 0.00
Fri 05/29 04Z 0.26 3424 90 41 2 0.00
Fri 05/29 05Z 0.27 3423 91 43 2 0.00
Fri 05/29 06Z 0.28 3421 91 49 2 0.00
Fri 05/29 07Z 0.32 3320 92 57 2 0.00
Fri 05/29 08Z 0.40 3319 92 68 2 0.00
Fri 05/29 09Z 0.42 3220 94 81 2 0.00
Fri 05/29 10Z 0.46 3219 95 85 2 0.01
Fri 05/29 11Z 0.43 3119 93 76 2 0.00
Fri 05/29 12Z 0.36 3118 87 81 3 0.00
Fri 05/29 13Z 0.28 3217 79 74 3 0.00
Fri 05/29 14Z 0.31 3216 74 67 3 0.00
Fri 05/29 15Z 0.48 3114 72 67 3 0.00
Fri 05/29 16Z 1.88 3011 69 76 4 0.00
Fri 05/29 17Z 4.11 2810 68 83 4 0.00
Fri 05/29 18Z 5.43 2512 70 83 5 0.00
Fri 05/29 19Z 6.19 2415 70 90 5 0.00
Fri 05/29 20Z 8.37 2417 67 90 6 0.00
Fri 05/29 21Z 4.59 2523 73 94 5 0.03
Fri 05/29 22Z 1.43 2424 76 91 4 0.01
Fri 05/29 23Z 1.34 2523 84 94 3 0.02
Sat 05/30 00Z 0.72 2321 91 95 4 0.08
Sat 05/30 01Z 0.66 2321 95 97 4 0.11
Sat 05/30 02Z 0.69 2617 97 93 3 0.13
Sat 05/30 03Z 0.63 3019 95 92 1 0.09
Sat 05/30 04Z 0.53 3119 91 79 0 0.03
Sat 05/30 05Z 0.40 3218 94 59 0 0.02
Sat 05/30 06Z 0.40 3216 95 43 -1 0.01
Sat 05/30 07Z 0.28 3315 97 52 -1 0.02
Sat 05/30 08Z 0.20 3516 97 63 -1 0.03
Sat 05/30 09Z 0.36 0218 97 74 -1 0.04
Sat 05/30 10Z 0.48 0424 98 87 -1 0.05
Sat 05/30 11Z 0.63 0528 97 84 -1 0.05
Run total areal avg QPF for the greens is: 0.87 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