Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260803_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)
=== ===== === ==== ==== === === === ====
Mon 08/03 18Z 0.77 2321  98  95  15 0.00
Mon 08/03 19Z 0.94 2524  98  91  14 0.07
Mon 08/03 20Z 1.03 2625  98  87  13 0.05
Mon 08/03 21Z 0.99 2726  98  91  12 0.06
Mon 08/03 22Z 0.91 2925  97  77  12 0.02
Mon 08/03 23Z 0.88 3027  97  63  11 0.02
Tue 08/04 00Z 0.78 3027  98  39  11 0.02
Tue 08/04 01Z 0.63 3128  95  52  10 0.02
Tue 08/04 02Z 0.37 3230  84  46  11 0.00
Tue 08/04 03Z 0.35 3229  77  23  11 0.00
Tue 08/04 04Z 0.58 3126  86  13  10 0.00
Tue 08/04 05Z 0.74 3026  83   3  10 0.00
Tue 08/04 06Z 0.73 2924  80   3  11 0.00
Tue 08/04 07Z 0.77 2924  74   4  11 0.00
Tue 08/04 08Z 0.74 2924  68   3  12 0.00
Tue 08/04 09Z 0.78 3025  66   2  12 0.00
Tue 08/04 10Z 0.77 3026  64   2  12 0.00
Tue 08/04 11Z 0.64 3025  59   2  12 0.00
Tue 08/04 12Z 0.54 3024  55   2  13 0.00
Tue 08/04 13Z 0.46 3022  53   2  13 0.00
Tue 08/04 14Z 0.43 3018  52   2  13 0.00
Tue 08/04 15Z 0.42 2914  52   2  13 0.00
Tue 08/04 16Z 0.41 2912  53   2  13 0.00
Tue 08/04 17Z 0.41 2809  56   2  13 0.00
Tue 08/04 18Z 0.46 2609  60   2  14 0.00
Tue 08/04 19Z 0.58 2608  62   2  14 0.00
Tue 08/04 20Z 0.55 2607  62   3  14 0.00
Tue 08/04 21Z 0.34 2606  61   3  15 0.00
Tue 08/04 22Z 0.25 2506  59   4  15 0.00
Tue 08/04 23Z 0.18 2505  54   4  16 0.00
Wed 08/05 00Z 0.16 2405  49   5  17 0.00
Wed 08/05 01Z 0.15 2305  46   6  17 0.00
Wed 08/05 02Z 0.18 2207  45   7  17 0.00
Wed 08/05 03Z 0.16 2207  44   8  17 0.00
Wed 08/05 04Z 0.16 2207  41   8  17 0.00
Wed 08/05 05Z 0.14 2206  37   8  17 0.00
Wed 08/05 06Z 0.15 2306  37   7  17 0.00
Wed 08/05 07Z 0.15 2406  38   6  17 0.00
Wed 08/05 08Z 0.15 2505  40   6  17 0.00
Wed 08/05 09Z 0.15 2505  43   6  16 0.00
Wed 08/05 10Z 0.16 2505  47   7  16 0.00
Wed 08/05 11Z 0.13 2504  45   7  16 0.00
Wed 08/05 12Z 0.13 2604  46   8  16 0.00
Wed 08/05 13Z 0.15 2605  51   9  15 0.00
Wed 08/05 14Z 0.16 2605  56   8  15 0.00
Wed 08/05 15Z 0.14 2304  57   6  15 0.00
Wed 08/05 16Z 0.15 2204  58   4  15 0.00
Wed 08/05 17Z 0.28 2206  59   2  15 0.00
Wed 08/05 18Z 0.43 2106  56   1  16 0.00
Wed 08/05 19Z 0.46 2208  51   1  16 0.00
Wed 08/05 20Z 0.33 2209  45   1  17 0.00
Wed 08/05 21Z 0.34 2309  44   2  17 0.00
Wed 08/05 22Z 0.38 2310  51   5  17 0.00
Wed 08/05 23Z 0.40 2411  59  12  17 0.00
Thu 08/06 00Z 0.40 2411  64  21  17 0.00
Thu 08/06 01Z 0.38 2410  67  26  17 0.00
Thu 08/06 02Z 0.34 2410  71  34  17 0.00
Thu 08/06 03Z 0.33 2410  73  49  17 0.00
Thu 08/06 04Z 0.32 2310  75  63  17 0.00
Thu 08/06 05Z 0.29 2311  77  73  17 0.00

Run total areal avg QPF for the Central_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