NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260930_1800
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 09/30 18Z 0.14 2505  99  29  11 0.00
Wed 09/30 19Z 0.15 2706  99  23  11 0.01
Wed 09/30 20Z 0.13 2806  99  27  11 0.01
Wed 09/30 21Z 0.14 2806  98  43  11 0.01
Wed 09/30 22Z 0.14 2806  95  53  11 0.00
Wed 09/30 23Z 0.16 2707  91  49  12 0.00
Thu 10/01 00Z 0.21 2609  88  48  12 0.00
Thu 10/01 01Z 0.29 2611  86  39  12 0.00
Thu 10/01 02Z 0.34 2613  87  29  12 0.01
Thu 10/01 03Z 0.38 2614  89  28  11 0.01
Thu 10/01 04Z 0.40 2715  91  33  11 0.01
Thu 10/01 05Z 0.38 2814  92  35  11 0.00
Thu 10/01 06Z 0.42 2714  94  40  11 0.00
Thu 10/01 07Z 0.44 2614  94  37  11 0.01
Thu 10/01 08Z 0.43 2514  95  40  12 0.01
Thu 10/01 09Z 0.41 2514  93  43  12 0.01
Thu 10/01 10Z 0.48 2417  93  63  12 0.01
Thu 10/01 11Z 0.49 2418  93  75  12 0.01
Thu 10/01 12Z 0.55 2319  93  80  12 0.01
Thu 10/01 13Z 0.59 2320  93  80  12 0.01
Thu 10/01 14Z 0.62 2322  92  84  12 0.00
Thu 10/01 15Z 0.73 2324  97  95  12 0.02
Thu 10/01 16Z 0.74 2323  95  95  12 0.02
Thu 10/01 17Z 0.70 2324  93  85  12 0.02
Thu 10/01 18Z 0.70 2422  89  74  13 0.00
Thu 10/01 19Z 0.77 2423  93  83  13 0.00
Thu 10/01 20Z 0.85 2425  91  94  13 0.00
Thu 10/01 21Z 0.75 2425  90  96  14 0.01
Thu 10/01 22Z 0.85 2428  86  93  14 0.01
Thu 10/01 23Z 0.90 2428  90  91  14 0.00
Fri 10/02 00Z 0.82 2427  89  85  14 0.01
Fri 10/02 01Z 0.88 2429  90  68  14 0.01
Fri 10/02 02Z 0.90 2332  89  47  15 0.00
Fri 10/02 03Z 1.00 2335  91  64  15 0.01
Fri 10/02 04Z 1.05 2436  90  86  15 0.03
Fri 10/02 05Z 1.06 2436  92  77  15 0.01
Fri 10/02 06Z 1.00 2435  89  80  15 0.01
Fri 10/02 07Z 0.96 2435  91  86  15 0.01
Fri 10/02 08Z 1.06 2436  93  87  15 0.04
Fri 10/02 09Z 1.04 2436  94  89  15 0.05
Fri 10/02 10Z 1.01 2534  95  88  15 0.04
Fri 10/02 11Z 0.97 2532  95  90  14 0.04
Fri 10/02 12Z 0.97 2531  97  94  14 0.07
Fri 10/02 13Z 0.81 2625  97  96  13 0.14
Fri 10/02 14Z 0.64 2821  98  95  13 0.11
Fri 10/02 15Z 0.52 2818  97  91  12 0.08
Fri 10/02 16Z 0.48 2816  97  78  12 0.02
Fri 10/02 17Z 0.47 2815  98  86  11 0.01
Fri 10/02 18Z 0.38 2913  97  85  11 0.02
Fri 10/02 19Z 0.33 2913  96  86  11 0.01
Fri 10/02 20Z 0.33 3014  94  80  10 0.03
Fri 10/02 21Z 0.37 3017  89  60  10 0.01
Fri 10/02 22Z 0.37 3018  89  50   9 0.00
Fri 10/02 23Z 0.39 3122  81  29   8 0.00
Sat 10/03 00Z 0.32 3123  76   8   8 0.00
Sat 10/03 01Z 0.31 3224  74   3   7 0.00
Sat 10/03 02Z 0.30 3224  85   2   6 0.00
Sat 10/03 03Z 0.30 3224  85   2   5 0.01
Sat 10/03 04Z 0.30 3224  89   2   5 0.00
Sat 10/03 05Z 0.24 3324  91   0   4 0.00

Run total areal avg QPF for the Central_Greens is: 0.98 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