Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260802_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)
=== ===== === ==== ==== === === === ====
Sun 08/02 18Z 0.30 1913  92  65  15 0.00
Sun 08/02 19Z 0.47 1914  91  57  15 0.04
Sun 08/02 20Z 0.49 1916  89  38  15 0.04
Sun 08/02 21Z 0.42 1819  88  35  15 0.01
Sun 08/02 22Z 0.33 1820  91  49  15 0.01
Sun 08/02 23Z 0.41 1921  89  49  15 0.01
Mon 08/03 00Z 0.31 1823  86  59  15 0.00
Mon 08/03 01Z 0.29 1824  84  72  16 0.00
Mon 08/03 02Z 0.28 1924  80  80  16 0.00
Mon 08/03 03Z 0.31 1924  84  84  15 0.01
Mon 08/03 04Z 0.31 1922  86  92  15 0.01
Mon 08/03 05Z 0.27 1921  86  90  16 0.01
Mon 08/03 06Z 0.24 1921  84  89  16 0.01
Mon 08/03 07Z 0.27 1922  88  76  16 0.01
Mon 08/03 08Z 0.28 1923  91  91  16 0.01
Mon 08/03 09Z 0.25 1922  90  84  17 0.01
Mon 08/03 10Z 0.20 1823  94  90  16 0.02
Mon 08/03 11Z 0.20 1825  95  85  16 0.09
Mon 08/03 12Z 0.35 1925  92  88  16 0.03
Mon 08/03 13Z 0.33 1923  94  86  16 0.01
Mon 08/03 14Z 0.38 1922  97  79  16 0.01
Mon 08/03 15Z 0.43 2022  98  82  16 0.01
Mon 08/03 16Z 0.56 2123  98  81  16 0.02
Mon 08/03 17Z 0.71 2123  98  74  16 0.02
Mon 08/03 18Z 0.77 2123  98  72  16 0.02
Mon 08/03 19Z 0.72 2122  96  80  16 0.08
Mon 08/03 20Z 0.70 2227  88  50  16 0.30
Mon 08/03 21Z 1.14 2329  97  52  14 0.02
Mon 08/03 22Z 1.20 2530  96  70  13 0.03
Mon 08/03 23Z 1.18 2731  97  76  12 0.05
Tue 08/04 00Z 0.96 2931  97  71  11 0.06
Tue 08/04 01Z 0.73 3029  97  80  11 0.04
Tue 08/04 02Z 0.58 3129  97  58  11 0.02
Tue 08/04 03Z 0.48 3128  93  30  10 0.00
Tue 08/04 04Z 0.38 3227  87  17  10 0.00
Tue 08/04 05Z 0.49 3126  83   5  10 0.00
Tue 08/04 06Z 0.62 3128  80   7  11 0.00
Tue 08/04 07Z 0.64 3129  77   4  11 0.00
Tue 08/04 08Z 0.63 3128  75   4  11 0.00
Tue 08/04 09Z 0.53 3126  70   3  12 0.00
Tue 08/04 10Z 0.49 3124  66   3  12 0.00
Tue 08/04 11Z 0.43 3022  63   3  12 0.00
Tue 08/04 12Z 0.35 3020  55   3  13 0.00
Tue 08/04 13Z 0.32 3019  51   2  14 0.00
Tue 08/04 14Z 0.31 3117  50   2  13 0.00
Tue 08/04 15Z 0.31 3015  49   2  14 0.00
Tue 08/04 16Z 0.26 3012  46   1  14 0.00
Tue 08/04 17Z 0.27 3010  47   1  14 0.00
Tue 08/04 18Z 0.23 2908  46   1  15 0.00
Tue 08/04 19Z 0.20 2906  44   1  16 0.00
Tue 08/04 20Z 0.18 2805  41   2  16 0.00
Tue 08/04 21Z 0.19 2705  40   2  16 0.00
Tue 08/04 22Z 0.19 2605  40   1  16 0.00
Tue 08/04 23Z 0.18 2405  42   1  16 0.00
Wed 08/05 00Z 0.22 2406  45   1  16 0.00
Wed 08/05 01Z 0.19 2406  43   1  16 0.00
Wed 08/05 02Z 0.18 2405  44   1  16 0.00
Wed 08/05 03Z 0.16 2305  43   1  16 0.00
Wed 08/05 04Z 0.10 2105  37   1  17 0.00
Wed 08/05 05Z 0.10 2006  33   1  17 0.00

Run total areal avg QPF for the Central_Greens is: 1.01 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