NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261001_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)
=== ===== === ==== ==== === === === ====
Thu 10/01 06Z 0.48 2713  91  70  10 0.00
Thu 10/01 07Z 0.56 2714  89  60  10 0.00
Thu 10/01 08Z 0.48 2713  89  52  10 0.00
Thu 10/01 09Z 0.49 2713  91  35  10 0.00
Thu 10/01 10Z 0.46 2511  90  38  10 0.00
Thu 10/01 11Z 0.37 2410  88  51  10 0.00
Thu 10/01 12Z 0.33 2212  89  71  10 0.00
Thu 10/01 13Z 0.38 2215  90  89  10 0.00
Thu 10/01 14Z 0.39 2118  92  92  10 0.00
Thu 10/01 15Z 0.45 2219  94  93  11 0.00
Thu 10/01 16Z 0.52 2221  94  91  11 0.01
Thu 10/01 17Z 0.56 2221  93  90  11 0.00
Thu 10/01 18Z 0.58 2222  89  84  12 0.00
Thu 10/01 19Z 0.61 2223  91  90  13 0.00
Thu 10/01 20Z 0.58 2324  93  95  13 0.01
Thu 10/01 21Z 0.63 2326  97  88  14 0.03
Thu 10/01 22Z 0.74 2427  97  64  14 0.02
Thu 10/01 23Z 0.81 2529  97  55  14 0.02
Fri 10/02 00Z 0.88 2630  96  69  14 0.02
Fri 10/02 01Z 0.82 2628  94  84  14 0.02
Fri 10/02 02Z 0.80 2628  93  84  14 0.02
Fri 10/02 03Z 0.78 2527  93  81  14 0.01
Fri 10/02 04Z 0.79 2429  92  76  14 0.01
Fri 10/02 05Z 0.77 2331  86  66  15 0.00
Fri 10/02 06Z 0.88 2337  87  67  15 0.00
Fri 10/02 07Z 0.97 2441  84  82  16 0.01
Fri 10/02 08Z 1.07 2442  82  86  15 0.02
Fri 10/02 09Z 1.06 2441  88  76  15 0.02
Fri 10/02 10Z 1.05 2439  94  83  15 0.04
Fri 10/02 11Z 1.06 2538  95  92  14 0.04
Fri 10/02 12Z 0.96 2533  97  95  14 0.06
Fri 10/02 13Z 0.93 2629  97  95  13 0.11
Fri 10/02 14Z 0.77 2724  97  91  13 0.09
Fri 10/02 15Z 0.53 2919  97  60  12 0.03
Fri 10/02 16Z 0.47 2919  96  38  12 0.02
Fri 10/02 17Z 0.42 2918  95  46  11 0.01
Fri 10/02 18Z 0.43 2920  92  40  10 0.01
Fri 10/02 19Z 0.42 2920  86  52  10 0.01
Fri 10/02 20Z 0.41 2919  79  38   9 0.00
Fri 10/02 21Z 0.42 3019  76  26   8 0.00
Fri 10/02 22Z 0.42 3120  72  11   7 0.00
Fri 10/02 23Z 0.47 3121  75   5   6 0.00
Sat 10/03 00Z 0.53 3122  79   5   5 0.00
Sat 10/03 01Z 0.71 3125  81   4   5 0.00
Sat 10/03 02Z 0.96 3225  81   7   4 0.00
Sat 10/03 03Z 0.91 3226  78  13   4 0.00
Sat 10/03 04Z 0.67 3225  80  19   4 0.00
Sat 10/03 05Z 0.62 3224  80  21   3 0.00
Sat 10/03 06Z 0.53 3223  81  15   3 0.00
Sat 10/03 07Z 0.46 3221  79  11   3 0.00
Sat 10/03 08Z 0.40 3219  80   9   2 0.00
Sat 10/03 09Z 0.45 3220  83   6   2 0.00
Sat 10/03 10Z 0.47 3220  83   4   2 0.00
Sat 10/03 11Z 0.33 3219  79   3   2 0.00
Sat 10/03 12Z 0.30 3218  76   3   2 0.00
Sat 10/03 13Z 0.26 3217  75   2   2 0.00
Sat 10/03 14Z 0.24 3215  70   2   2 0.00
Sat 10/03 15Z 0.26 3215  68   2   2 0.00
Sat 10/03 16Z 0.25 3214  62   3   2 0.00
Sat 10/03 17Z 0.26 3213  60   5   2 0.00

Run total areal avg QPF for the greens is: 0.64 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