NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260304_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)
=== ===== === ==== ==== === === === ====
Wed 03/04 06Z 0.37 2817  97  57  -3 0.00
Wed 03/04 07Z 0.32 3018  90  38  -2 0.00
Wed 03/04 08Z 0.30 3019  76  48  -1 0.01
Wed 03/04 09Z 0.28 3019  60  37   0 0.01
Wed 03/04 10Z 0.29 3018  50  22   0 0.01
Wed 03/04 11Z 0.32 3018  47  15   0 0.01
Wed 03/04 12Z 0.38 2920  47  12   0 0.00
Wed 03/04 13Z 0.45 2922  49  11   0 0.00
Wed 03/04 14Z 0.49 2924  44  10   0 0.00
Wed 03/04 15Z 0.48 3024  46   9   0 0.00
Wed 03/04 16Z 0.39 3021  50   7   0 0.00
Wed 03/04 17Z 0.34 2917  57   7   0 0.00
Wed 03/04 18Z 0.35 2815  61   9   0 0.00
Wed 03/04 19Z 0.38 2815  61  10   0 0.00
Wed 03/04 21Z 0.45 2717  58  15   0 0.00
Wed 03/04 22Z 0.47 2618  57  17   0 0.00
Wed 03/04 23Z 0.47 2719  55  21   1 0.00
Thu 03/05 01Z 0.48 2720  54  26   1 0.00
Thu 03/05 02Z 0.45 2719  54  27   1 0.00
Thu 03/05 03Z 0.40 2718  51  26   2 0.00
Thu 03/05 04Z 0.42 2718  53  28   1 0.00
Thu 03/05 06Z 0.40 2817  59  24   0 0.00
Thu 03/05 07Z 0.38 2916  64  23   0 0.00
Thu 03/05 08Z 0.37 2916  67  21   0 0.00
Thu 03/05 09Z 0.35 2915  70  19   0 0.00
Thu 03/05 10Z 0.33 2815  72  19   0 0.00
Thu 03/05 11Z 0.26 2912  73  19   0 0.00
Thu 03/05 12Z 0.22 2911  73  20   0 0.00
Thu 03/05 13Z 0.17 3009  74  21   0 0.00
Thu 03/05 14Z 0.12 3007  76  23   0 0.00
Thu 03/05 15Z 0.08 3004  78  25   0 0.00
Thu 03/05 16Z 0.06 2903  79  26   0 0.00
Thu 03/05 17Z 0.04 2801  80  25   0 0.00
Thu 03/05 18Z 0.04 1800  82  26   0 0.00
Thu 03/05 19Z 0.05 1401  83  25   0 0.00
Thu 03/05 20Z 0.08 1303  86  26   0 0.00
Thu 03/05 21Z 0.13 1205  89  26  -1 0.00
Thu 03/05 22Z 0.16 1207  91  26  -1 0.00
Thu 03/05 23Z 0.14 1309  90  26  -1 0.00
Fri 03/06 00Z 0.13 1310  86  26   0 0.00
Fri 03/06 01Z 0.12 1311  82  28   0 0.00
Fri 03/06 02Z 0.13 1312  81  29   0 0.01
Fri 03/06 03Z 0.14 1313  81  30   0 0.01
Fri 03/06 04Z 0.15 1415  81  32   0 0.01
Fri 03/06 05Z 0.15 1415  79  33   0 0.01
Fri 03/06 06Z 0.16 1417  78  34   0 0.01
Fri 03/06 07Z 0.16 1417  79  35   0 0.01
Fri 03/06 08Z 0.13 1416  83  39   0 0.01
Fri 03/06 09Z 0.13 1516  85  41   0 0.01
Fri 03/06 10Z 0.11 1515  86  42   0 0.01
Fri 03/06 11Z 0.10 1515  88  41  -1 0.00
Fri 03/06 12Z 0.11 1515  88  40   0 0.00
Fri 03/06 13Z 0.11 1515  89  35   0 0.00
Fri 03/06 14Z 0.09 1515  91  35   0 0.00
Fri 03/06 15Z 0.10 1516  92  33   0 0.00
Fri 03/06 16Z 0.10 1516  92  30   0 0.00
Fri 03/06 17Z 0.09 1616  93  29   0 0.00

Run total areal avg QPF for the greens is: 0.13 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