NAM12 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM12 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM12_20260202_0600
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)
=== ===== === ==== ==== === === === ====
Mon 02/02 06Z 0.11 3425  62  25 -10 0.00
Mon 02/02 09Z 0.09 3428  46  26  -8 0.00
Mon 02/02 12Z 0.08 3425  41  21  -8 0.00
Mon 02/02 15Z 0.09 3423  40  16  -9 0.00
Mon 02/02 18Z 0.14 3320  38  12  -9 0.00
Mon 02/02 21Z 0.22 3322  41  18  -9 0.00
Tue 02/03 00Z 0.21 3321  39  41  -9 0.00
Tue 02/03 03Z 0.12 3315  38  60  -8 0.00
Tue 02/03 06Z 0.15 3211  41  51  -9 0.00
Tue 02/03 09Z 0.21 3011  45  38  -9 0.00
Tue 02/03 12Z 0.17 2808  42  13  -9 0.00
Tue 02/03 15Z 0.17 2507  42  42 -10 0.00
Tue 02/03 18Z 0.19 2309  65  91 -10 0.00
Tue 02/03 21Z 0.32 2510  86  53 -12 0.00
Wed 02/04 00Z 0.63 2612  95  64 -14 0.00
Wed 02/04 03Z 0.90 2614  86  72 -14 0.00
Wed 02/04 06Z 0.90 2618  90  67 -14 0.00
Wed 02/04 09Z 0.79 2719  85  92 -16 0.00
Wed 02/04 12Z 0.54 2918  84  67 -16 0.00
Wed 02/04 15Z 0.40 3015  88  53 -16 0.00
Wed 02/04 18Z 0.34 3012  84  35 -15 0.00
Wed 02/04 21Z 0.35 2911  77  32 -14 0.00
Thu 02/05 00Z 0.36 3014  82  26 -13 0.00
Thu 02/05 03Z 0.34 3012  81  31 -14 0.00
Thu 02/05 06Z 0.25 2809  91  37 -14 0.00
Thu 02/05 09Z 0.31 2810  93  41 -16 0.00
Thu 02/05 12Z 0.35 2911  91  54 -17 0.00
Thu 02/05 15Z 0.54 3014  88  81 -18 0.03
Thu 02/05 18Z 6.40 3015  91  76 -19 0.01

Run total areal avg QPF for the greens is: 0.04 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