The first Thursday in May is National Day of Prayer ; this year, that day is May 4th, tomorrow.
The law establishing an annual day of prayer was passed in 1952: by it, the president was required to set aside and proclaim a suitable day each year, other than a Sunday, as National Day of Prayer. In 1988, the law was amended  to direct the president to set aside and proclaim the first Thursday in May in each year for such purpose.
The current text of the law is found at 36 U.S.C. §119. National Day of Prayer :
The President shall issue each year a proclamation designating the first Thursday in May as a National Day of Prayer on which the people of the United States may turn to God in prayer and meditation at churches, in groups, and as individuals.
The theme for this year’s observance is “For Your Great Name’s Sake! Hear Us… Forgive Us…Heal Us!”, based on Daniel 9:19 .
This year, Dr. Dave Butts, chairman of the board of the National Day of Prayer Task Force, has proffered  the following ideas as “Prayers for America” (quotations from Msgr. Knox’s translation at New Advent):
- Protection: “Let every devout soul, then, turn to thee in prayer when hard times befall; rise the floods never so high, they shall have no power to reach it. Thou art my hiding-place, when I am sore bestead; songs of triumph are all about me, and thou my deliverer.” (Psalm 32:6- 7)
- Presence: “I will make my dwelling among you, and never shall my love cast you off, still coming and going in the midst of you, I your God, and you my people.” (Levitcus 26:11-12 )
- Peace: “Securely you shall hold your lands; sleep safe in your beds, with peace on all your frontiers. I will rid you, too, of ravenous beasts, and never the sword shall lay your country waste.” (Leviticus 26:5b-6 )
- Provision: “He, the Lord, is kind and merciful. In abundance he fed the men who feared him, keeping his covenant for ever. Lordly the power he shewed his people, making the lands of the heathen their possession.” (Psalm 111:5-7a )
- Proficiency: “Here is a word of advice for thee; do but listen, and God will speed thee. Thy part is to be the representative of this people with God, referring all their affairs to him, prescribing to them rite and observance, custom to be kept and duty to be done. Meanwhile, choose out here and there among the people able men, God-fearing, lovers of truth and haters of gain ill won; put each of these in charge of a tribe, or of a hundred families, or fifty families, or ten. These will administer justice to the people from day to day, referring graver matters to thee, but deciding for themselves all that is of less moment. Share thy burden with others, and find relief; so thou wilt be able to carry out God’s commands, and endure the weight of all his claims upon thee, and yet all these folk will go home satisfied.” (Exodus 18:19-23 )