Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260610_0600
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 06/10 06Z 0.32 2710  72   1  16 0.00
Wed 06/10 07Z 0.36 2710  75   7  15 0.00
Wed 06/10 08Z 0.34 2709  79  28  15 0.01
Wed 06/10 09Z 0.27 2707  80  56  15 0.00
Wed 06/10 10Z 0.21 2505  81  74  15 0.00
Wed 06/10 11Z 0.26 2208  82  82  15 0.00
Wed 06/10 12Z 0.27 2209  85  84  15 0.00
Wed 06/10 13Z 0.28 2210  89  83  15 0.00
Wed 06/10 14Z 0.30 2111  91  81  15 0.00
Wed 06/10 15Z 0.35 2111  92  88  15 0.00
Wed 06/10 16Z 0.36 2011  91  83  16 0.00
Wed 06/10 17Z 0.35 1911  91  87  16 0.00
Wed 06/10 18Z 0.69 2012  91  91  16 0.01
Wed 06/10 19Z 0.89 2116  90  93  16 0.02
Wed 06/10 20Z 0.51 2118  90  93  16 0.01
Wed 06/10 21Z 0.64 2119  89  86  16 0.00
Wed 06/10 22Z 0.69 2116  89  87  16 0.00
Wed 06/10 23Z 0.59 2115  91  88  16 0.00
Thu 06/11 00Z 0.44 2115  94  88  16 0.07
Thu 06/11 01Z 0.49 2118  98  91  16 0.10
Thu 06/11 02Z 0.55 2219  96  85  16 0.17
Thu 06/11 03Z 0.61 2321  97  89  16 0.11
Thu 06/11 04Z 0.51 2417  95  76  16 0.12
Thu 06/11 05Z 0.56 2418  95  81  16 0.03
Thu 06/11 06Z 0.57 2618  96  79  16 0.03
Thu 06/11 07Z 0.63 2620  97  79  16 0.02
Thu 06/11 08Z 0.57 2719  95  71  16 0.01
Thu 06/11 09Z 0.55 2719  95  63  16 0.01
Thu 06/11 10Z 0.54 2719  94  74  16 0.01
Thu 06/11 11Z 0.53 2819  95  70  15 0.01
Thu 06/11 12Z 0.46 2816  94  71  16 0.00
Thu 06/11 13Z 0.48 2816  94  69  16 0.00
Thu 06/11 14Z 0.39 2814  90  40  17 0.00
Thu 06/11 15Z 0.25 2910  83  19  17 0.00
Thu 06/11 16Z 0.30 2909  84  50  17 0.00
Thu 06/11 17Z 0.53 2710  87  62  17 0.00
Thu 06/11 18Z 0.56 2711  91  57  17 0.00
Thu 06/11 19Z 0.58 2613  96  70  17 0.03
Thu 06/11 20Z 0.55 2714  94  66  17 0.02
Thu 06/11 21Z 0.59 2615  95  70  18 0.01
Thu 06/11 22Z 0.55 2816  86  68  18 0.00
Thu 06/11 23Z 0.60 2815  91  73  17 0.00
Fri 06/12 00Z 0.59 2915  92  68  17 0.00
Fri 06/12 01Z 0.50 2814  95  68  16 0.06
Fri 06/12 02Z 0.41 2914  96  51  16 0.12
Fri 06/12 03Z 0.32 2913  93  42  16 0.01
Fri 06/12 04Z 0.29 2913  89  43  17 0.00
Fri 06/12 05Z 0.24 3012  90  52  17 0.00
Fri 06/12 06Z 0.25 3012  89  61  16 0.00
Fri 06/12 07Z 0.33 2914  92  61  16 0.00
Fri 06/12 08Z 0.38 2916  96  64  15 0.01
Fri 06/12 09Z 0.38 3017  96  64  15 0.01
Fri 06/12 10Z 0.33 3014  94  71  15 0.01
Fri 06/12 11Z 0.30 3013  88  79  16 0.00
Fri 06/12 12Z 0.26 3011  87  74  16 0.00
Fri 06/12 13Z 0.24 2909  83  56  16 0.00
Fri 06/12 14Z 0.12 2905  71  38  18 0.00
Fri 06/12 15Z 0.14 2805  67  24  18 0.00
Fri 06/12 16Z 0.27 2707  69  27  18 0.00
Fri 06/12 17Z 0.27 2808  64  33  18 0.00

Run total areal avg QPF for the Central_Greens is: 1.02 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