Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260611_1800
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 06/11 18Z 0.94 2805  90  55  16 0.00
Thu 06/11 19Z 1.18 2707  88  56  16 0.00
Thu 06/11 20Z 1.10 2708  88  60  17 0.00
Thu 06/11 21Z 0.64 2609  91  64  17 0.00
Thu 06/11 22Z 0.50 2609  92  66  17 0.05
Thu 06/11 23Z 0.42 2709  91  70  17 0.00
Fri 06/12 00Z 0.31 2709  82  76  18 0.02
Fri 06/12 01Z 0.25 2807  76  73  18 0.00
Fri 06/12 02Z 0.33 2609  75  75  18 0.00
Fri 06/12 03Z 0.40 2510  81  75  18 0.00
Fri 06/12 04Z 0.45 2412  86  74  18 0.00
Fri 06/12 05Z 0.36 2311  86  67  18 0.00
Fri 06/12 06Z 0.34 2410  83  63  18 0.00
Fri 06/12 07Z 0.31 2409  82  64  18 0.00
Fri 06/12 08Z 0.31 2509  85  71  17 0.00
Fri 06/12 09Z 0.27 2708  89  71  17 0.00
Fri 06/12 10Z 0.18 2806  91  76  17 0.00
Fri 06/12 11Z 0.10 3002  91  71  17 0.00
Fri 06/12 12Z 0.08 2501  93  75  17 0.00
Fri 06/12 13Z 0.08 2302  95  75  16 0.00
Fri 06/12 14Z 0.13 2304  95  74  16 0.00
Fri 06/12 15Z 0.14 2204  92  58  17 0.00
Fri 06/12 16Z 0.15 2104  89  56  17 0.00
Fri 06/12 17Z 0.41 2205  87  49  17 0.00
Fri 06/12 18Z 1.11 2306  83  46  18 0.00
Fri 06/12 19Z 1.66 2306  79  39  18 0.00
Fri 06/12 20Z 2.62 2308  80  34  18 0.00
Fri 06/12 21Z 1.71 2310  82  19  18 0.00
Fri 06/12 22Z 0.77 2212  84  46  18 0.00
Fri 06/12 23Z 0.65 2316  92  79  18 0.01
Sat 06/13 00Z 0.81 2620  87  65  17 0.14
Sat 06/13 01Z 0.73 2722  76  62  17 0.02
Sat 06/13 02Z 0.65 2824  65  46  16 0.01
Sat 06/13 03Z 0.60 2823  71  24  15 0.01
Sat 06/13 04Z 0.55 2924  66  11  15 0.00
Sat 06/13 05Z 0.54 3025  60  11  14 0.00
Sat 06/13 06Z 0.51 3025  59  10  14 0.00
Sat 06/13 07Z 0.49 3026  58  10  14 0.00
Sat 06/13 08Z 0.48 3025  60  13  13 0.00
Sat 06/13 09Z 0.45 3025  60  14  13 0.00
Sat 06/13 10Z 0.41 3125  61  13  13 0.00
Sat 06/13 11Z 0.40 3124  62  14  13 0.00
Sat 06/13 12Z 0.47 3124  64  17  12 0.00
Sat 06/13 13Z 0.50 3121  65  14  12 0.00
Sat 06/13 14Z 0.55 3018  66  13  12 0.00
Sat 06/13 15Z 0.63 3015  65  11  12 0.00
Sat 06/13 16Z 1.71 2913  70   7  11 0.00
Sat 06/13 17Z 4.61 2713  77   7  11 0.00
Sat 06/13 18Z 6.56 2713  79  11  12 0.00
Sat 06/13 19Z 7.21 2713  75  15  12 0.00
Sat 06/13 20Z 7.86 2713  71  15  13 0.00
Sat 06/13 21Z 5.98 2712  66  18  13 0.00
Sat 06/13 22Z 3.33 2611  64  19  13 0.00
Sat 06/13 23Z 1.26 2512  62  27  14 0.00
Sun 06/14 00Z 1.18 2515  61  46  14 0.00
Sun 06/14 01Z 1.08 2518  61  54  14 0.00
Sun 06/14 02Z 0.94 2519  61  45  14 0.00
Sun 06/14 03Z 0.73 2518  57  43  14 0.00
Sun 06/14 04Z 0.58 2517  51  43  15 0.00
Sun 06/14 05Z 0.62 2519  44  41  15 0.00

Run total areal avg QPF for the greens is: 0.26 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