Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260621_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)
=== ===== === ==== ==== === === === ====
Sun 06/21 06Z 0.43 2912  87  77   8 0.00
Sun 06/21 07Z 0.44 2914  88  74   8 0.00
Sun 06/21 08Z 0.47 2915  92  77   8 0.00
Sun 06/21 09Z 0.48 2917  95  86   7 0.01
Sun 06/21 10Z 0.44 2916  95  95   7 0.01
Sun 06/21 11Z 0.45 2917  93  79   7 0.00
Sun 06/21 12Z 0.49 2917  93  77   7 0.00
Sun 06/21 13Z 0.49 2916  91  78   7 0.00
Sun 06/21 14Z 0.46 2915  91  80   8 0.00
Sun 06/21 15Z 0.51 3015  93  85   7 0.00
Sun 06/21 16Z 0.49 3115  95  90   7 0.01
Sun 06/21 17Z 0.58 3114  95  90   8 0.01
Sun 06/21 18Z 0.51 3213  92  89   8 0.00
Sun 06/21 19Z 0.42 3114  88  90   8 0.03
Sun 06/21 20Z 0.59 3113  80  75   9 0.05
Sun 06/21 21Z 0.78 3012  80  74   9 0.00
Sun 06/21 22Z 0.58 3012  82  66   9 0.00
Sun 06/21 23Z 0.57 2912  87  67   9 0.00
Mon 06/22 00Z 0.55 2914  88  76   9 0.02
Mon 06/22 01Z 0.46 3013  89  72   9 0.06
Mon 06/22 02Z 0.35 3113  87  66   9 0.00
Mon 06/22 03Z 0.28 3113  86  60   9 0.00
Mon 06/22 04Z 0.27 3112  88  60   9 0.00
Mon 06/22 05Z 0.21 3111  87  46   9 0.00
Mon 06/22 06Z 0.16 3210  82  31  10 0.00
Mon 06/22 07Z 0.16 3209  82  31   9 0.00
Mon 06/22 08Z 0.15 3107  81  31   9 0.00
Mon 06/22 09Z 0.18 2905  82  31   9 0.00
Mon 06/22 10Z 0.21 2805  81  33   9 0.00
Mon 06/22 11Z 0.24 2706  79  32   9 0.00
Mon 06/22 12Z 0.17 2804  77  28   9 0.00
Mon 06/22 13Z 0.05 2701  74  25   9 0.00
Mon 06/22 14Z 0.03 1702  78  23   9 0.00
Mon 06/22 15Z 0.09 1805  81  25   9 0.00
Mon 06/22 16Z 0.41 1908  82  47   9 0.00
Mon 06/22 17Z 0.16 1810  76  90   9 0.01
Mon 06/22 18Z 0.22 1911  84  94   8 0.03
Mon 06/22 19Z 0.11 1511  89  95   8 0.06
Mon 06/22 20Z 0.23 1418  89  99   8 0.06
Mon 06/22 21Z 0.33 1422  89  99   9 0.04
Mon 06/22 22Z 0.39 1429  96  99   9 0.09
Mon 06/22 23Z 0.37 1434  97  99  11 0.13
Tue 06/23 00Z 0.24 1535  98  98  12 0.13
Tue 06/23 01Z 0.19 1633  96  91  12 0.34
Tue 06/23 02Z 0.22 1832  95  90  13 0.17
Tue 06/23 03Z 0.28 1930  97  89  13 0.21
Tue 06/23 04Z 0.33 1930  98  93  13 0.17
Tue 06/23 05Z 0.38 2030  99  91  14 0.13
Tue 06/23 06Z 0.46 2028  99  93  14 0.28
Tue 06/23 07Z 0.44 2124 100  95  13 0.19
Tue 06/23 08Z 0.45 2220  99  86  13 0.14
Tue 06/23 09Z 0.44 2417  99  95  12 0.06
Tue 06/23 10Z 0.35 2817  98  86  12 0.04
Tue 06/23 11Z 0.34 3021  97  61  11 0.02
Tue 06/23 12Z 0.34 3125  96  44   9 0.02
Tue 06/23 13Z 0.35 3228  94  26   9 0.02
Tue 06/23 14Z 0.34 3227  92  24   9 0.01
Tue 06/23 15Z 0.41 3225  94  21   8 0.01
Tue 06/23 16Z 0.55 3123  95  23   8 0.01
Tue 06/23 17Z 0.63 3121  93  19   8 0.01

Run total areal avg QPF for the Central_Greens is: 2.58 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