NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260805_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)
=== ===== === ==== ==== === === === ====
Wed 08/05 12Z 0.23 2607  74  38  15 0.00
Wed 08/05 13Z 0.21 2606  74  37  15 0.00
Wed 08/05 14Z 0.16 2504  72  35  15 0.00
Wed 08/05 15Z 0.20 2304  71  33  15 0.00
Wed 08/05 16Z 0.28 2104  71  29  15 0.00
Wed 08/05 17Z 0.50 2106  71  23  15 0.00
Wed 08/05 18Z 0.76 2207  70  17  15 0.00
Wed 08/05 19Z 0.64 2207  67  12  16 0.00
Wed 08/05 20Z 0.64 2208  64  10  16 0.00
Wed 08/05 21Z 0.53 2208  63  11  16 0.00
Wed 08/05 22Z 0.51 2309  68  13  16 0.00
Wed 08/05 23Z 0.54 2310  75  16  15 0.00
Thu 08/06 00Z 0.51 2310  78  20  15 0.00
Thu 08/06 01Z 0.51 2311  80  26  15 0.00
Thu 08/06 02Z 0.51 2311  80  26  15 0.00
Thu 08/06 03Z 0.50 2312  81  22  15 0.00
Thu 08/06 04Z 0.45 2313  83  23  16 0.00
Thu 08/06 05Z 0.45 2314  84  25  16 0.00
Thu 08/06 06Z 0.47 2315  86  38  16 0.00
Thu 08/06 07Z 0.44 2415  85  50  16 0.01
Thu 08/06 08Z 0.39 2413  83  52  16 0.01
Thu 08/06 09Z 0.35 2411  82  49  16 0.00
Thu 08/06 10Z 0.30 2410  83  46  16 0.00
Thu 08/06 11Z 0.23 2309  83  47  16 0.00
Thu 08/06 12Z 0.19 2208  83  59  16 0.00
Thu 08/06 13Z 0.17 2207  85  70  16 0.00
Thu 08/06 14Z 0.20 2207  88  82  16 0.00
Thu 08/06 15Z 0.24 2207  90  78  16 0.00
Thu 08/06 16Z 0.28 2206  91  71  16 0.00
Thu 08/06 17Z 0.38 2206  90  76  16 0.00
Thu 08/06 18Z 0.42 2207  89  72  16 0.00
Thu 08/06 19Z 0.44 2206  88  72  17 0.00
Thu 08/06 20Z 0.39 2206  87  72  17 0.00
Thu 08/06 21Z 0.35 2207  87  75  17 0.01
Thu 08/06 22Z 0.24 2207  88  74  17 0.04
Thu 08/06 23Z 0.32 2309  87  77  17 0.08
Fri 08/07 00Z 0.37 2310  90  73  17 0.11
Fri 08/07 01Z 0.42 2411  86  61  17 0.10
Fri 08/07 02Z 0.49 2613  86  42  17 0.02
Fri 08/07 03Z 0.48 2715  89  49  17 0.01
Fri 08/07 04Z 0.49 2716  85  51  17 0.02
Fri 08/07 05Z 0.46 2716  78  60  17 0.00
Fri 08/07 06Z 0.45 2716  72  67  17 0.00
Fri 08/07 07Z 0.44 2716  68  65  17 0.00
Fri 08/07 08Z 0.42 2816  72  66  17 0.00
Fri 08/07 09Z 0.37 2914  73  59  17 0.00
Fri 08/07 10Z 0.34 3014  78  63  16 0.00
Fri 08/07 11Z 0.31 3013  81  65  16 0.00
Fri 08/07 12Z 0.30 3013  83  71  16 0.00
Fri 08/07 13Z 0.27 3112  84  72  16 0.00
Fri 08/07 14Z 0.24 3110  84  69  16 0.00
Fri 08/07 15Z 0.22 3109  83  70  16 0.00
Fri 08/07 16Z 0.21 3007  85  70  16 0.00
Fri 08/07 17Z 0.26 2905  85  72  16 0.00
Fri 08/07 18Z 0.38 2805  85  73  16 0.00
Fri 08/07 19Z 0.53 2705  85  73  16 0.00
Fri 08/07 20Z 0.43 2605  84  73  16 0.00
Fri 08/07 21Z 0.31 2605  83  71  17 0.00
Fri 08/07 22Z 0.29 2506  84  71  17 0.00
Fri 08/07 23Z 0.28 2407  84  71  17 0.00

Run total areal avg QPF for the greens is: 0.41 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