Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260701_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 07/01 12Z 0.21 3112  77  57  18 0.00
Wed 07/01 13Z 0.23 3012  79  48  18 0.00
Wed 07/01 14Z 0.23 3010  76  38  18 0.00
Wed 07/01 15Z 0.28 2909  73  24  18 0.00
Wed 07/01 16Z 0.42 2808  73  18  18 0.00
Wed 07/01 17Z 0.73 2708  72  17  18 0.00
Wed 07/01 18Z 1.00 2508  72  19  18 0.00
Wed 07/01 19Z 1.10 2409  75  31  19 0.00
Wed 07/01 20Z 1.52 2411  79  46  19 0.00
Wed 07/01 21Z 0.98 2314  80  47  19 0.00
Wed 07/01 22Z 0.83 2417  87  46  19 0.00
Wed 07/01 23Z 0.97 2423  91  54  19 0.00
Thu 07/02 00Z 0.94 2522  87  52  20 0.00
Thu 07/02 01Z 0.80 2624  78  51  20 0.00
Thu 07/02 02Z 0.63 2823  82  50  20 0.00
Thu 07/02 03Z 0.61 2722  78  50  20 0.00
Thu 07/02 04Z 0.61 2723  77  54  20 0.00
Thu 07/02 05Z 0.53 2822  68  52  21 0.00
Thu 07/02 06Z 0.50 2821  70  54  21 0.00
Thu 07/02 07Z 0.53 2822  81  60  20 0.00
Thu 07/02 08Z 0.46 2820  79  63  20 0.00
Thu 07/02 09Z 0.40 2919  83  62  20 0.00
Thu 07/02 10Z 0.36 2918  81  61  19 0.00
Thu 07/02 11Z 0.31 2916  74  52  20 0.00
Thu 07/02 12Z 0.30 3017  70  55  20 0.00
Thu 07/02 13Z 0.35 2918  70  43  20 0.00
Thu 07/02 14Z 0.40 2918  75  42  19 0.00
Thu 07/02 15Z 0.45 2917  78  49  19 0.00
Thu 07/02 16Z 0.53 2916  82  53  19 0.00
Thu 07/02 17Z 0.55 2815  82  56  19 0.00
Thu 07/02 18Z 0.54 2716  75  59  20 0.00
Thu 07/02 19Z 0.81 2718  83  59  20 0.00
Thu 07/02 20Z 1.14 2619  88  55  19 0.00
Thu 07/02 21Z 1.04 2520  93  46  19 0.00
Thu 07/02 22Z 1.05 2622  90  46  20 0.01
Thu 07/02 23Z 1.04 2623  85  39  20 0.01
Fri 07/03 00Z 1.01 2624  88  44  20 0.01
Fri 07/03 01Z 1.02 2626  88  63  20 0.00
Fri 07/03 02Z 1.06 2728  92  69  19 0.01
Fri 07/03 03Z 0.96 2728  91  65  19 0.04
Fri 07/03 04Z 0.89 2728  87  59  19 0.01
Fri 07/03 05Z 0.87 2829  82  58  19 0.00
Fri 07/03 06Z 0.76 2929  74  60  19 0.00
Fri 07/03 07Z 0.66 2928  70  54  18 0.00
Fri 07/03 08Z 0.61 2927  70  44  19 0.00
Fri 07/03 09Z 0.53 2926  67  40  19 0.00
Fri 07/03 10Z 0.46 3026  60  40  19 0.00
Fri 07/03 11Z 0.42 3024  60  36  19 0.00
Fri 07/03 12Z 0.39 3021  57  33  19 0.00
Fri 07/03 13Z 0.37 2919  55  34  19 0.00
Fri 07/03 14Z 0.40 2918  50  48  19 0.00
Fri 07/03 15Z 0.53 2818  56  45  18 0.00
Fri 07/03 16Z 0.64 2819  60  64  18 0.00
Fri 07/03 17Z 1.01 2719  73  63  18 0.00
Fri 07/03 18Z 6.00 2718  77  69  17 0.00
Fri 07/03 19Z 8.46 2718  77  64  17 0.00
Fri 07/03 20Z 6.21 2818  79  68  17 0.00
Fri 07/03 21Z 3.06 2819  80  61  18 0.03
Fri 07/03 22Z 1.99 2919  80  41  18 0.00
Fri 07/03 23Z 1.23 2919  78  31  18 0.00

Run total areal avg QPF for the Central_Greens is: 0.12 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