Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260611_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)
=== ===== === ==== ==== === === === ====
Thu 06/11 18Z 1.00 2905  87  55  17 0.00
Thu 06/11 19Z 1.38 2806  86  54  17 0.00
Thu 06/11 20Z 1.36 2608  86  57  17 0.00
Thu 06/11 21Z 0.71 2508  89  62  17 0.00
Thu 06/11 22Z 0.53 2609  91  66  17 0.08
Thu 06/11 23Z 0.47 2610  91  70  17 0.01
Fri 06/12 00Z 0.29 2709  78  77  18 0.03
Fri 06/12 01Z 0.25 2707  71  71  19 0.00
Fri 06/12 02Z 0.39 2610  74  73  18 0.00
Fri 06/12 03Z 0.51 2512  83  74  18 0.00
Fri 06/12 04Z 0.54 2414  88  69  18 0.00
Fri 06/12 05Z 0.38 2412  85  61  18 0.00
Fri 06/12 06Z 0.30 2410  79  58  19 0.00
Fri 06/12 07Z 0.25 2408  78  56  19 0.00
Fri 06/12 08Z 0.23 2507  81  66  18 0.00
Fri 06/12 09Z 0.19 2706  87  67  17 0.00
Fri 06/12 10Z 0.10 3004  88  76  17 0.00
Fri 06/12 11Z 0.05 0102  88  68  17 0.00
Fri 06/12 12Z 0.03 3401  92  72  17 0.00
Fri 06/12 13Z 0.04 2801  94  75  16 0.00
Fri 06/12 14Z 0.10 2602  95  75  16 0.00
Fri 06/12 15Z 0.12 2203  92  65  17 0.00
Fri 06/12 16Z 0.14 2103  88  55  17 0.01
Fri 06/12 17Z 0.51 2204  85  50  17 0.00
Fri 06/12 18Z 1.51 2306  81  53  18 0.00
Fri 06/12 19Z 2.18 2306  77  42  18 0.00
Fri 06/12 20Z 3.47 2409  79  35  18 0.00
Fri 06/12 21Z 2.02 2410  83  23  18 0.00
Fri 06/12 22Z 0.88 2313  85  44  18 0.00
Fri 06/12 23Z 0.76 2317  91  78  18 0.02
Sat 06/13 00Z 0.84 2520  89  60  17 0.02
Sat 06/13 01Z 0.73 2722  82  61  16 0.03
Sat 06/13 02Z 0.60 2824  56  50  17 0.01
Sat 06/13 03Z 0.52 2923  63  13  16 0.00
Sat 06/13 04Z 0.43 3023  61  10  15 0.00
Sat 06/13 05Z 0.39 3024  54  10  15 0.00
Sat 06/13 06Z 0.40 3025  53  10  14 0.00
Sat 06/13 07Z 0.39 3126  52   9  14 0.00
Sat 06/13 08Z 0.38 3126  53  11  13 0.00
Sat 06/13 09Z 0.36 3126  53  11  13 0.00
Sat 06/13 10Z 0.31 3126  56  12  13 0.00
Sat 06/13 11Z 0.27 3225  55  12  13 0.00
Sat 06/13 12Z 0.32 3224  60  16  12 0.00
Sat 06/13 13Z 0.36 3122  65  14  12 0.00
Sat 06/13 14Z 0.42 3118  64  13  12 0.00
Sat 06/13 15Z 0.49 3016  61  13  12 0.00
Sat 06/13 16Z 1.04 2913  66   9  12 0.00
Sat 06/13 17Z 3.99 2812  76   5  12 0.00
Sat 06/13 18Z 6.14 2713  79   6  12 0.00
Sat 06/13 19Z 7.17 2712  76  10  13 0.00
Sat 06/13 20Z 7.90 2713  73  13  13 0.00
Sat 06/13 21Z 6.39 2711  68  17  13 0.00
Sat 06/13 22Z 3.95 2611  66  14  14 0.00
Sat 06/13 23Z 1.47 2511  65  17  14 0.00
Sun 06/14 00Z 1.38 2515  64  38  14 0.00
Sun 06/14 01Z 1.05 2518  63  50  14 0.00
Sun 06/14 02Z 0.89 2519  63  43  14 0.00
Sun 06/14 03Z 0.69 2518  60  43  15 0.00
Sun 06/14 04Z 0.54 2517  53  42  15 0.00
Sun 06/14 05Z 0.60 2519  44  37  15 0.00

Run total areal avg QPF for the Central_Greens is: 0.21 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